Question 152127
Given {{{3a=c-a(b+d)}}}
First use distribution to expand the right side
{{{3a=c-ab -ad}}}
Now move all the terms with an 'a' in them to the same side
{{{3a + ab + ad = c}}} Basically we added ab+ad to both sides
Now use distribution to pull the a out of the three terms on the left side
{{{a*(3+b+d) = c}}}
Now divide both sides by (3+b+d) 
{{{a = c / (3+b+d)}}}