$(15$ points$)$ A linear system is described by the differential equation $($with input x$($t$)$ and output y$($t$))$: dy$($t$)$ dt $+10$y$($t$)=$ x$($t$).(3)$ What is the transfer function of the system? Determine the steady$-$state response if x$($t$)=2$ cos$(20$t$)$u$($t$).$