area of the bottom square = 11*9 =99 squre inches
for the triangular top the area = 1/2 x b x h
you have hypotenuse and height so need to calculate the base dimension
4^2 +x^2 = 7^2
16 +x^2 = 49
x^2 = 33 x = sqrt(33) = 5.7
area = 1/2 4*5.7 = 11.489
there are two similar triangles so 11.489*2 = 22.97
99+22.97 = 121.97
looks like they rounded the numbers slightly different
so 121 in2 is their answer