If Lucy would give Linda $5, Lucy would have the same amount of money as Linda. If Lucy originally had $20, how much money did Linda have at the beginning?
After giving $5, Lucy has $20 - $5 = $<T>subtract(20, 5)=15 left.
Since Linda has $15 after receiving $5, then she had $15 - $5 = $<T>subtract(15, 5)=10 at the beginning.
