Let x and y be integers. Show that 9x + 5y is divisible by 19 if and only if x + 9y is divisible by 19.
I would really appircate some help, I'm stuck on this problem!
x must be 1 (up to mod 19) and y must be 2 (mod 19). Therefore, x + 9y = 1 + 2*9 = 19 = 0 (mod 19).
