QRST is a square use the properties of a square to find the value of x

The sides of a square are equal. This means that
QR = RS = ST = QT
Given that
QR = 7x - 10 and RS = 5x + 2, we can say that
7x - 10 = 5x + 2
By collecting like terms, we have
7x - 5x = 2 + 10
2x = 12
x = 12/2
x = 6