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You say the mass is 350 kg, then you say it is 50 kg ?
I will assume mass = m
You are evidently assuming g = 10 m/s^2. However to be safe I will just call it g.
Component of weight down slope = m g sin 60 = 0.866 m g
Component of weight normal to surface = m g cos 60 = 0.500 m g
friction force down slope mu m g cos 60 = 0.500 m g mu
These are balanced by pull force F up slope
F = (0.866 + 0.500 mu) m g
work done to pull up = F * d = F * 20/sin 60 = 23 F
= 23 (0.866 + 0.500 mu) m g Joules