Concept:Modular arithmetic finds the remainder after division by the given modulus.Explanation:First, compute the product: 23×54.23×54=1242.Now divide 1242 by the modulus 7.7×177=1239.Subtract: 1242−1239=3.This remainder is 3, so the product is congruent to 3(mod7).Therefore, 23×54≡3(mod7).Answer:3Option B.