A square model has 25a² + 60a + 36. What are the side of the small corner and the side of the large part, respectively?

Correct answer: 6 and 5a

The direct answer is A: the small corner has side 6 and the large part has side 5a. In a square-area model, a square with area 25a² has side √(25a²)=5a, while a square with area 36 has side √36=6. The middle term confirms the arrangement: two rectangles each have area (5a)(6)=30a, giving 60a altogether. Thus the expression is (5a+6)² = 25a²+60a+36. Option B lists the same two lengths in the reverse order, but the question asks for the small corner first. Option C gives area values rather than side lengths, and 25a is not the side obtained from 25a². Option D does not square to the required first and last terms. The key habit is to take square roots of the square tiles and then check the two cross-rectangles.