I think I understand. Steve and Laura initially had crayons in a ratio of 7:2. After Steve gives Laura 15 of his crayons, the both have equal amounts. Then, we want to know their final amounts? Or their initial amounts? I guess I will just answer both.
Let's write what we know in algebraic language. I will use "/" to mean division. I will use S for Steve's initial amount and L for Laura's initial amount.
S / L = 7 / 2
S - 15 = L + 15
I would use substitution. So, first solve the second equation for S in terms of L.
S = L + 30
Now, substitute into the first equation.
(L + 30) / L = 7 / 2
Multiply both sides by 2*L.
2*(L + 30) = 7 * L
2L + 60 = 7L
Subtract 2L from both sides.
60 = 5L
Divide both sides by 5.
12 = L
Laura started with 12 crayons. Steve started with 30 more (Remember S = L + 30), so Steve began with 42 crayon. Indeed, we should check that 42/12 = 7/2.
After the transfer of crayons, they each would have 27 crayons.