Use the Crank$-$Nicholson method to approximate the solution of the boundary$-$

value problem

$n=8m=300\mathrm{.}25\frac{de{l}^{2}u}{del{x}^2}=\frac{\text{d}\text{e}\text{l}\text{u}}{\text{d}\text{e}\text{l}\text{t}},0$

using $n=8$ and $m=30.$