Given data:
* The weight of the block A is 44 N.
* The weight of the block B is 22 N.
* The coefficient of static friction between A and table is 0.20.
Solution:
(a). The weight of the A and C block is balanced by the weight of the block B.
Thus, the friction force acting on the Block A in terms of the weight of the Block B is,

This describe the static friction force acting on the Block A ( with block C above it) in contact with the table.
where W_AC is the combined weight of block A and C, W_B is the weight of the block B, and

Substituting the known values,

Thus, the minimum weight of the block C in terms of combined weight is,

Hence, the minimum weight of the block C is 66 N.