Question 74143
{{{15-a/3=-9}}}
{{{-a/3=-9-15}}}Subtract 15 from both sides
{{{-a=3(-9-15)}}}Multiply both sides by 3
{{{-a=-27-45)}}}Distribute the 3 to each term
{{{-a=-72}}}Subtract like terms
{{{-1(-a)=-1(-72)}}}Multiply both sides by -1
{{{a=72}}}
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Check:
{{{15-a/3=-9}}}Plug in a=72 
{{{15-72/3=-9}}}
{{{15-24=-9}}}
{{{-9=-9}}}Works