Which expression is equivalent to 9 x^2 + 7 x^2 + 9 x ?

The correct answer is D. Choice D is correct. In the given expression, the first two terms, 9 x^2 and 7 x^2 , are like terms. Combining these like terms yields 9 x^2 + 7 x^2 , or 16 x^2 . It follows that the expression 9 x^2 + 7 x^2 + 9 x is equivalent to 16 x^2 + 9 x .