2510^4 elevator is to be accelerated upward by connecting it to a counterweight using a light (but strong!) cable passing over a solid uniform...

A 2.25×10^4 elevator is to be accelerated upward by connecting it to a counterweight using a light (but strong!) cable passing over a solid uniform disk-shaped pulley. There is no appreciable friction at the axle of the pulley, but its mass is 900 kg and it is 1.50 m in diameter.How heavy should the counterweight be so that it will accelerate the elevator upward through 6.75 in the first 3.50 , starting from rest?