turn scientific to fixed

[ramin.lich]

hi all
ok this is my code

void MainWindow::on_pushButton_2_clicked()
{
    QString b;
   float x,y,z;
   x=ui->lineEdit_3->text().toLong();
   y=ui->lineEdit_4->text().toLong();
   z=x*y;
   z=(float)z/100;
   cout<<fixed;
   ui->textBrowser_2->setText(b.setNum(z));
 
}

void MainWindow::on_pushButton_2_clicked()
{
    QString b;
   float x,y,z;
   x=ui->lineEdit_3->text().toLong();
   y=ui->lineEdit_4->text().toLong();
   z=x*y;
   z=(float)z/100;
   cout<<fixed;
   ui->textBrowser_2->setText(b.setNum(z));

}

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i dont know why still show me scientific format in textBrowser?!?
any help will be grateful.