First of all there are multiple formula's to get the volume of a trapezoidal prism:
V=(1/2 * (base1 + base2) * h) * height prism
Using the numbers you gave:
base1 = 7 base2 = 5 h = 4 height prism = 8
Putting this into the equation: V=(1/2 * (7 + 5) * 4) * 8
V= (1/2 * 12 * 4) * 8
V = 24 * 8
V = 192
The volume of the gift box is 191 inches squared.
