Question

Jan is as old now as Gary was $15$ years ago. Six years from now, Gary will be twice as old as Jan will be then. How old is Gary now?

Answer 1

(1)J=G-15
G+6=2(J+6), G+6=2J+12,  (2)G=2J+6
(2) substitute in (1)

J=2J+6-15
-J=-9
J=9
9=G-15
G=24 now Gary