There are six towers which are each 24 blocks tall. bob the builder wishes to merge them into a tower which is 144 blocks tall. in a move, bob may take a block from any tower (say with a blocks) and move it on top of any other tower (say with b blocks), as long as a ≤ b. due to gravity, the effort of doing so takes bob b − a 2 hours. determine the minimum amount of time it takes bob to construct a tower of height 144.