SAT Question 18c7c3e0: Equivalent Expressions answer and explanation with Desmos solution

Choice B is correct. Since each term in the given expression has a common factor of $x^2$, it can be rewritten as $(13-7)x^2$, or $6x^2$. Therefore, the expression $6x^2$ is equivalent to $13x^2-7x^2$.

Alternate approach: Since the two terms of the given expression are both constant multiples of $x^2$, they are like terms and can, therefore, be combined through subtraction. Subtracting like terms in the expression $13x^2-7x^2$ yields $6x^2$.