20 * 19 * 18 * 17 * 16 * 15 * 14 * 13 * 12 * 11 * 10 * 9 * 8 * 7 * 6 * 5 * 4 *3 *2 *1
15 * 14 * 13 * 12 * 11 * 10 * 9 * 8* 7 *6 *5 * 4 * 3 * 2 * 1
ok so now u take out what is in common that leaves u with :
20 * 19 * 18 * 17 * 16 * 15 = 27,907,200
15 * 14 = 210
27,907,200 / 210 = 132,891.4286
hope this helps:)