$2.($U & G$-$required$)[40$ points$]$ Solve the following recurrences using the method

indicated:

a$)[20$ points$]$ T$($n$)=2$T$($n$/4)+$ n using the recursion tree method.

b$)[20$ points$]$ Show by substitution that T$($n$)=2$T$($n$/4)+1$ is O$($n$)$