Here PQ is the height QR is the base.
Since the side of the square is given as 5 cm
∴BC = 5 cm and PQ = AB = 5 cm
QR = BC - (BQ + CR)
BQ = AP = 1 cm
Hence
QR = 5-[1+1]
= 5 - 2
= 3 cm
Area of triangle =12×base×height
Area of triangle PQR =12×QR×PQ
=12[3×5]
=152
=7.5 cm2