Answer:
 140 in^3
Step-by-step explanation:
The volume formula can be written as ...
 A = Bh
Marcia found B = 20 in^2, so we can use that in the formula, along with h = 7 in.
 A = (20 in^2)(7 in)
 A = 140 in^3
The volume of the box is 140 cubic inches.