attn mechanical engineers or physic gurus

Can anyone help me solve this dynamics question?
By Using the Work-energy method
(PE1+KE1)+-W=(PE2+KE2)
PE = mgh
KE = m*v^2*1/2
w = F*S

A System of a 120kg trolley and a 100kg counter weight is show (refer pic) calculate the correct load that can be:
(a) raised in the trolley
(b) lowered in the trolley
at constant velocity
Assume tha the resistance to motion is proportional to the mass of the loaded trolley.....

I've been stuck on this days. It would be good if someone could help. thanks