Respuesta :
I'm assuming that this is what your diagram looks like because these types of problems always look like this (lol).
Comment if you need clarification!
Comment if you need clarification!

Answer:
a) Force required to keep both the masses in rest will be - 77 N
b) The coefficient of friction will be 0.55
Explanation:
a) As the weight of 77 N is suspended vertically so, there must act 77 N force on the 140 N weight to keep both masses in rest. Hence, the answer is -77 N.
b) We know that:
140µ = 77
µ = 77/140
µ = 0.55
Hence, the minimum co-efficient of friction required to keep both bodies in rest will be 0.55.