Question 862677
I made the correction below with what I think you meant.
{{{9a+6b=-9}}}
{{{-9a+b=30}}}
Add the equations together.
{{{9a+6b-9a+b=-9+30}}}
{{{7b=21}}}
{{{b=3}}}
Then use either equation to solve for {{{a}}}
{{{9a+18=-9}}}
{{{9a=-27}}}
{{{a=-3}}}