Question 216540
is that {{{(15-a)/3 = 9}}} or {{{15 - (a/3) = 9}}}??
The way you stated it, it is {{{15 - (a/3) = 9}}} so we'll solve that one
{{{15 - (a/3) = 9}}}
{{{(45 - a)/3 = 9}}} 
{{{45 - a = 27}}}
{{{45 - 27 = a}}}
{{{18 = a}}}
If the problem was {{{(15-a)/3 = 9}}}
Then
{{{(15-a)/3 = 9}}}
{{{(15-a) = 27}}}
{{{15-27 = a}}}
{{{-12 = a}}}