This question hinges on HCF concepts. So since the cuboid is made of 784 cubes, the volume of the cuboid is 784cm3. Hence, by using HCF, we find out what are the possible prime factors that make up 784. The next hint: is the perimeter, so using the prime factors we obtained, we can find the best combination that makes length+breadth = 15. Therefore, solving the height at the end.