$7.$A$.$ An $8\mathrm{.}0$ kg box has speed of $25$m$/$s at point B at the bottom of the frictionless plane inclined at $20$ with respect to the horizontal plane, which has a coefficient of friction $=0\mathrm{.}10$ along the length BC $=5\mathrm{.}0$ m$.$ Point A is $2\mathrm{.}5$ m above the plane. There is no friction on the slope CD a$.$ What is its speed at point A$?$ b$.$ What is the speed at point C$?$ c$.$ How high will the box travel along the slope CD before it will stop?