Base of the prism is a right-angled triangle having its base and altitude as 12 cm and 16 cm, respectively.
Hence, the third side will be equal to:
√122+162=√144+256=√400=20 cm
Total area = Lateral surface area + Area of 2 triangles (base and top)
Total area =12×22+16×22+20×22+2×12×12×16
=22(12+16+20)+12×16
=1,056+192
=1,248 cm2