element.py

import sys
from PyQt5 import QtCore, QtGui, uic

qtCreatorFile = 'untitled.ui' #window File
Ui_MainWindow,QtBaseClass = uic.loadUiType(qtCreatorFile)

class App(QtGui.QMainWindow,Ui_MainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        Ui_MainWindow.__init__(self)
        self.setupUi(self)
        self.btnSub.clicked.connect(self.CalculateTax)
    def CalculateTax(self):
        price = int(self.textPrice.toPlainText())
        tax = float(self.dSBPer.value())
        total_price = price - ((tax/100) * price)
        total_price_string = u'Do you can\'t to what money?:' + str(total_price)
        self.labelResult.setText(total_price_string)

if __name__ == '__main__':
    app = QtGui.QGuiApplication(sys.argv)
    window = App()
    window.show()
    sys.exit(app.exec_())