To determine the number of cubes he needs to fill the box (this is assuming the cubes are 1 in cubes, he would need to calculate the volume of the box. To find the volume he would multiply the length by the width by the height. This would be 5 in x 6 in x 7 in. The volume is 210 cubic inches, so he could fill it with 210 one inch cubes.
I think you can put bench mark place valie round tenth thousnadth
7(x - 3) + 3(4 - x) = -8
7x - 21 + 12 - 3x = -8
7x - 3x = -8 + 21 - 12
4x = 1
x = 1/4
