Question 971764
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I assume the equation is:
{{{y=z/(z-a)}}} (If the equation is {{{y=z/z-a}}}, you cannot solve for z.) Multiply each side by (z-a). 
{{{y(z-a)=z}}}
{{{yz-ya=z}}} Add ya to each side.
{{{yz=z+ya}}} Subtract z from each side.
{{{yz-z=ya}}}
{{{z(y-1)=ya}}} Divide each side by (y-1)
{{{z=(ya)/(y-1)}}}