Work Energy And Power

A particle of mass $M$ moves along a horizontal $x$ axis from $x=0$ to $x=L$. The coefficient of kinetic friction varies as a function of $x$ as $\mu_k(x)=\mu_0-\alpha x$, where $\mu_0$, $\alpha$ are constants of appropriate dimensions, so that $\mu_k(L)=0$. The total work done by the frictional force during the motion is $n \mu_0 M g L$, where $g$ is the acceleration due to gravity. The value of $n$ is: