The model has a square of area y², two equal strips of area 5y each, and a small corner square of area 25. It represents the square of what?

Correct answer: (y + 5)²

The correct answer is A: (y + 5)². Begin with the pieces of the area model. The large square has area y², so its side is y. Each strip has area 5y, which comes from side lengths y and 5. Since there are two strips, their combined area is 5y + 5y = 10y. The corner is a 5 by 5 square, so its area is 25. Therefore the complete area is y² + 10y + 25. Using the identity (a + b)² = a² + 2ab + b² with a = y and b = 5 gives (y + 5)² = y² + 10y + 25. Option A matches every part of the model. Option B would give y² − 10y + 25 and would require subtracting strips, not adding them. Option C is the square of 5y, which is 25y², and does not describe this four-part model. Option D would produce y² + 50y + 625, so both its middle and constant terms are wrong. Memory cue: two positive equal strips mean the middle term is +2ab.