Hi, can I get help with this?

How much work is done lifting a 20 pound object from the ground to the top of a 45 foot building if the cable used weighs 2.5 pounds per foot?

I used the formula work = integral from a to b F(x) dx.

F(x) = 20 + ((45 ft * 2.5 lbs/ft) - 2.5 lbs/ft x = 112.5 - 2.5x

Then w = integral from 0 to 20 (112.5 - 2.5x) = 1750 foot-lbs.

But this was incorrect?

Thank you!