Question 407938
If 3x + 11 ≡ 13 (mod 17) then 3x ≡ 2 (mod 17). Hence, 3x = 2, 19, 36, ... and the smallest positive integer that satisfies is 3x = 36 --> x = 12. 


We can easily check since 3(12) + 11 = 47 ≡ 13(mod 17).