Question

by which expression should(15am+3an+5bm+bn) be divided to get (3a+b)

Answer 1

$let \: the \: expression \: be \: x \\ then \: (15am + 3an + 5bm + bn) \div x = (3a + b) \\ or \: x = 3a(5m + n) + b(5m + n) \div (3a + b) \\ or \: x = (3a + b)(5m + n) \div (3a + b) \\ or \: x = (5m + n)$