Explanation:
9a = (12a + 3b)/4
to solve for b means we transform the equation so that we end up with
b = ...
or
... = b
remember, whatever we do, we always have to so it to both sides of the equation. otherwise we destroy its information.
the most disturbing thing in an expression is always a division or fraction.
so, let's get rid of it by multiplying everything by 4 :
4×9a = 4×(12a + 3b)/4
36a = 12a + 3b
now, let's bring everything that is not a term in b to the other side of b. that means we subtract 12a from both sides :
36a - 12a = 12a + 3b - 12a
24a = 3b
and now, to get only b in one side, we simply divide everything by 3 :
24a/3 = 3b/3
8a = b
tadaaaa !
b = 8a