Solve the following recurrence relation.

$($a$)x_{k+2}-4x_{k+1}+4x_k=3,$ where $x_0=1,x_1=0$

$($b$)x_{k+2}+5x_{k+1}+6x_k=2^{k+2},$ where $x_0=0,x_1=2$

$($c$)x_{k+2}-9x_k=2k,$ where $x_0=1,x_1=1$