Block A (70 N) and block B (21 N) are connected by a massless cord and are at rest. Given ìs = 0.8. What is friction A ?

Answer 1

What is 0.8? The coefficient of friction? Static or kinetic?

If they are at rest on a horizontal plane, and the cord is unstretched, friction is zero. In some situations (incline or stretched cord) there can be static friction sufficient to maintain equilibrium.

You have not fully defined the problem.

Answer 2

56N