Answer:
315
Step-by-step explanation:
If i understand this correctly, you just need to get the volume of the box and divide it by the volume of the 1/2 cube to see how many will fit.
# 1/2in cubes = (5.25 * 3 * 2.5)/(0.5 * 0.5 * 0.5)
# 1/2in cubes = (39.375)/(0.125) = 315
