20. If 7x=6 mod 5. Then the value of x is: A. 2 B. 3 C. 4 D. 5

To solve this problem, we need to find the value of x that satisfies the given congruence equation.The congruence equation states that 7x is congruent to 6 modulo 5. This means that when 7x is divided by 5, the remainder is 6.To find the value of x, we can use the properties of modular arithmetic. Specifically, we can use the fact that if a ≡ b (mod m), then a ≡ b + km (mod m) for any integer k.In this case, we can rewrite the congruence equation as:7x ≡ 6 (mod 5)To isolate x, we can multiply both sides of the equation by the modular inverse of 7 modulo 5. The modular inverse of 7 modulo 5 is 3, since 7 * 3 ≡ 1 (mod 5).Multiplying both sides of the equation by 3, we get:(3 * 7)x ≡ (3 * 6) (mod 5)Simplifying, we have:21x ≡ 18 (mod 5)Since 21 ≡ 1 (mod 5) and 18 ≡ mod 5), we can rewrite the equation as:x ≡ 3 (mod 5)This means that x is congruent to 3 modulo 5, which implies that x = 5k + 3 for some integer k.Therefore, the correct answer is B. 3.