How much work is required to wind the entire chain on the pulley?

An 80ft length of steel chain weighing 20lb/ft is dangling from a pulley. How much work is required to wind the entire chain on the pulley? In this problem you are to EVALUATE the integral required to answer the question.

change in energy = integral 0 to 80 of 20xdx
the integral = 10x^2+constant
the constant = 0 since 0 work done at 0 feet

10x^2 = 64000-0=64000ft lbs