If given integers a and b where a ≡ 7 (mod 20) and b ≡ −3 (mod 4), determine the integer c by 0 ≤ c ≤ 20 such that c ≡ 2a + b (mod 12)

Question

My initial approach involves transforming the given congruences into linear equations:

a ≡ 7 (mod 20) to a = 20k + 7

b ≡ −3 (mod 4) to b = 4m - 3

then I plug that into the congruence of c getting:

c ≡ 40k + 14 + 4m - 3 (mod 12)

c ≡ 4k + m + 11 (mod 12)

What should I do next?