$[6]$ Initially a $12\mathrm{.}00$ kg block slides on a frictionless horizontal surf$$ with a constant speed of $3\mathrm{.}75\frac{m}{s}.$ Then the block encounters a new region of the horizontal surface where there is friction: the coefficient of kinetic friction is $0\mathrm{.}245.$ The block comes to rest.

$=>$ be careful of $+$ and $-$ in this problem.

HINT: first find the friction force.

a$)$ How far does the block slide along the surface with friction? $($use forces & kinematics$)$

b$)$ Use the definition of work to find the amount of work done by the friction force.

c$)$ Use the work energy theorem to calculate the amount of work done.