The diagonals of a parallelogram will bisect each other....so we have
PT = TR and QT = TS
So...we have this system
y = 4x + 1 (1)
2y = 5x + 8 (2)
Sub (1) into (2) and we have that
2 ( 4x + 1) = 5x + 8
8x + 2 = 5x + 8
8x - 5x = 8 - 2
3x = 6 → x = 2
And
y = 4(2) + 1 = 9