Help with alignment

Hi,

Im having trouble in aligning my QComboBox, and my exit button. I want them to be like the image that i have attached (in the center, in the right hand corner of the window), i have aligned them, but i must've did something wrong.

Here is my code:
Code:
#include <QLabel>
#include <QPushButton>
#include <QGraphicsView>
#include <QLineEdit>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QPushButton>
#include <QApplication>
#include <QCheckBox>
#include <QSpacerItem>
#include <QLineEdit>
#include <QGroupBox>
 #include <QComboBox>
#include "browseimages.h"
 
BrowseImages::BrowseImages(QWidget *parent) : QWidget(parent)
{
	//  Title of the window
	this->setWindowTitle("Image Browser");	
	this->resize(700, 400); 
 
	b_search = new QPushButton(tr("SEARCH"));
 
	b_exit = new QPushButton(tr("Exit"));
 
	combo = new QComboBox (this);
 
	   QHBoxLayout *h_exit = new QHBoxLayout;
	h_exit->addStretch();
	h_exit->addWidget(b_exit);
	h_exit->addStretch();
 
    connect(b_exit, SIGNAL(clicked()), qApp, SLOT(quit()));
 
	l_welcome = new QLabel(tr("--Image Browser--"));
 	l_welcome->setFont(QFont("Times", 18, QFont::Bold));
	l_welcome->setAlignment(Qt::AlignCenter);
 
	g_graphics = new QGraphicsView(this);
 
    t_box = new QGroupBox(this);
    //t_box= new QGroupBox(tr("Tool Box"));
    t_box->setFixedSize(150,270);
 
 
	QHBoxLayout *v_g = new QHBoxLayout;
	v_g->setAlignment(Qt::AlignCenter);
	v_g->addWidget(g_graphics);
	v_g->addWidget(t_box);
 
	QHBoxLayout *v_e = new QHBoxLayout;
	v_e->setAlignment(Qt::AlignRight);
	v_e->addWidget(combo);
 
	QHBoxLayout *v_m= new QHBoxLayout;
	v_m->setAlignment(Qt::AlignRight);
	v_m->addWidget(b_exit);
 
	/*QHBoxLayout *v_w= new QHBoxLayout;
	v_w->setAlignment(Qt::AlignRight);
	v_w->addWidget(v_e);
	v_w->addWidget(v_m);*/
 
 
 
    //--------------------------------//
	QHBoxLayout *sub1 = new QHBoxLayout;
	sub1->setAlignment(Qt::AlignRight);
	cb1= new QCheckBox(tr("Search By Plate Number"));   
    sub1->addWidget(cb1);
 
   	QHBoxLayout *sub2 = new QHBoxLayout;
	sub2->setAlignment(Qt::AlignRight);
    l1= new QLineEdit(this);
    sub2->addWidget(l1);
 
    QHBoxLayout *sub3 = new QHBoxLayout;
	sub3->setAlignment(Qt::AlignLeft);
	cb2= new QCheckBox(tr("Search By Date"));
	sub3->addWidget(cb2);
 
 
    QHBoxLayout *sub4 = new QHBoxLayout;
	sub4->setAlignment(Qt::AlignLeft);
	l2= new QLineEdit(this);
    sub4->addWidget(l2);
 
    QHBoxLayout *sub5 = new QHBoxLayout;
	sub5->setAlignment(Qt::AlignCenter);
	b_ok= new QPushButton(tr("OK"));
	b_ok->setFixedHeight(20);
    sub5->addWidget(b_ok);
 
 
    QVBoxLayout *mainsub = new QVBoxLayout;
	mainsub->setAlignment(Qt::AlignRight);
	mainsub->addLayout(sub1);
	mainsub->addLayout(sub2);
	mainsub->addSpacing(40);
	mainsub->addLayout(sub3);
	mainsub->addLayout(sub4);
	mainsub->addLayout(sub5);
    t_box->setLayout(mainsub);
 
    //------------------------------------------//
 
 
	QVBoxLayout *layout_vert = new QVBoxLayout;
	layout_vert->setAlignment(Qt::AlignCenter);
	layout_vert->addWidget(l_welcome);
	layout_vert->addLayout(v_g);
	layout_vert->addLayout(v_e);
	layout_vert->addSpacing(20);
	layout_vert->addLayout(v_m);
	this->setLayout(layout_vert);
    }
Thank you very much.