Math Distribution Help

If 6(x+y)(x-y)=60 and x-y=30, what is the value of x+y?

Im studying for the SAT and I dont know how to do this one!

Well, first let a=x+y, which is what you're looking for. Then, let b=x-y=30.
Plug these into the equation:

6(x+y)(x-y)=60
6(a)(b)=60
6(a)(30)=60
180a=60
a=1/3
x+y=1/3

So 1/3 is your answer. Basically all you had to do was plug that value into the equation they give you and solve for the whole expression rather than each variable individually.

Since x - y = 30, you can substitute 30 for the (x-y) into the left side:

6(x + y) * (x - y) = 60
6(x + y) * 30 = 60 (divide both sides by 30)
6(x + y) = 2 (now divide both sides by 6)
x + y = 2/6 = 1/3