$12-4\mathrm{.}4.$ The compound wheel shown in Fig. P$-12-4\mathrm{.}4$ rolls without slipping. At the given position, the velocity of A is $6$fps and the acceleration of A is $20$fps$^2,$ both directed to the right. Compute the acceleration of points B and C$.$

ab $=65\mathrm{.}6$fps$^2$ ; ac $=36$fps$^2$