# SAT Math Multiple Choice Question 929: Answer and Explanation

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**Question: 929**

**13.** If (*x*, *y*) is a solution to the system of equations above, what is the value of *y*^{2}?

- A. 12
- B. 16
- C. 120
- D. 144

**Correct Answer:** D

**Explanation:**

**D**

**Difficulty:** Medium

**Category:** Passport to Advanced Math / Quadratics

**Strategic Advice:** When you encounter a system of equations in which one of the equations is already solved for a variable, substitute its value into the other equation and solve.

**Getting to the Answer:** The second equation tells you that *y* is equal to 3*x*, so substitute 3*x* for *y* in the first equation. Then solve for *x*^{2} (not *x* because *x*^{2} will be more useful when solving for *y*^{2}):

Now, substitute 16 for *x*^{2} in the first equation and solve for *y*^{2}:

The correct answer is (D).