Problem $4.($Need help, solve all$)$ Find the following limits:

$($a$)\underset{x3}{lim}\frac{x^2-x-6}{x-3},$

$($b$)\underset{x0}{lim}\frac{(6+x{)}^2-36}{x},$

$($c$)\underset{x-3}{lim}\frac{\sqrt[\phantom{2}]{(2x+22)}-4}{x+3},$

$($d$)\underset{x3}{lim}\frac{9-x^2}{\sqrt[\phantom{2}]{3-x}}.$