Concept:For two overlapping sets P and Q, the size of their union equals the sum of their individual sizes minus the size of their intersection.Explanation:Use the formula: n(P∪Q)=n(P)+n(Q)−n(P∩Q).Substitute the given values: n(P)=19, n(P∪Q)=38, and n(P∩Q)=7.So, 38=19+n(Q)−7.Simplify the constant terms: 19−7=12.Thus, 38=12+n(Q).Subtract 12 from both sides: n(Q)=38−12.Therefore, n(Q)=26.Answer:26Option A is correct.