well i cannot see the box... but I can tell you how to solve the exercise.
imagine the box has height H, width W and Length L
the volume of said box would be V = H*W*L
now imagine that Carla's box was similar to this one.
and she filled this box with 1 cm cubes, assuming the height to be 3 cm
v= (number of cubes height) *(number of cubes width) *(number of cubes length) = 3 * 3 * 5 cubic cm= 45 cubic cm
