$6\mathrm{.}3.$ Given the difference equation y$($n$)$ x$($n $1)-0\mathrm{.}75$y$($n $1)-0\mathrm{.}125$y$($n $2)$ a$.$ calculate the system response y$($n$)$ for n $0,1,...,4$ with the input x$($n$)=(0\mathrm{.}5)"$u$($n$)$ and initial conditions: x$(-1)=-1,$ y$(2)2,$ and y$(-1)=1$; b$.$ calculate the system response y$($n$)$ for n $-0,1,...,4$ with the input x$($n$)(0\mathrm{.}5)"$u$($n$)$ and zero initial conditions: x$(-1)=0,$ y$(-2)=0,$ and y$(-1)=0.$