A digital system is described by the following difference equation:

y$(7)=0\mathrm{.}25$x$(7-2)+0\mathrm{.}5$y$(7-1)-0\mathrm{.}2$y$(72-2)$

Find the transfer function H$($z$),$ the denominator polynomial A$($z$),$ and the numerator poly$-\_$nomial B$($z$).$