Question 928272
Take your pick.  Choose an equation and solve for a variable in terms of the other variable.  Neither equation is right or wrong to choose first; neither variable is right or wrong to solve as formula first.  


An easy way to begin, is take the simpler equation and solve for either variable in terms of the other variable, and then substitute into the other equation.
{{{x=1-y}}}
-
{{{8(1-y)+5y=-13}}}
{{{8-8y+5y=-13}}}
{{{8-3y=-13}}}
{{{8+13=3y}}}
{{{3y=21}}}
{{{highlight_green(y=7)}}}
Do the rest.