Machines A, B, and C do the same amount of work, but they each take a different amount of time. Machine A takes more time as compared to machine C. Machine B takes the maximum time to do the same amount of work. Which machine expends the most power doing this work?

So power is considered as the rate of doing work. Base on the problem given, my analysis is that the machine who finish the work faster is machine C. Therefore, in order to finish the same amount of work in a short period of time you are going to expend the most power. My answer is Machine C.