Two blocks A and B shown in $($Figure $1)$ have a weight of $11$ lb and $6$ lb$,$ respectively. They are resting on the incline for which the coefficients of static friction are A $=0\mathrm{.}15$ and B $=0\mathrm{.}25.$ Determine the angle which will cause motion of one of the blocks. What is the friction force under each of the blocks when this occurs? The spring has a stiffness of k $=2$ lb$/$ft and is originally unstretched.

A$.$ Determine the smallest angle which will cause motion of one of the blocks.

B$.$ Determine is the friction force under the block A at this angle.

C$.$ Determine is the friction force under the block B at this angle.