Tim had 504 local and foreign stamps altogether. He had 2/7 as many foreign stamps as local stamps. For every 28 local stamps he had, his mother gave him 6 more local stamps. After his father gave him some foreign stamps, the total number of local stamps he had became 1 1/3 times that of foreign stamps. How many foreign stamps. How many foreign stamps did his father give him?
f + L = 504
f = 2 L/7
so
2 L/7 + 7 L/7 = 504
9 L/7 = 504
L = 392
f = 2 * 392 / 7
so
f = 112
(112 + ff ) (4/3) = L