Answer
a). $30^{\circ}$
b). $0.577$
Work Step by Step
As per result of problem 73,
coefficient of static friction = $tan\theta$
a). The angle is independent of the mass or contact area. So, the angle will be same as in the case of the smaller box. So, $\theta=30^{\circ}$
b). Coefficient of friction =$tan30^{\circ}=0.577$
