# SAT Math Multiple Choice Question 678: Answer and Explanation

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**Question: 678**

**3.** A certain function takes an input value and transforms it into an output value according to the following three-step procedure:

Step 1: Multiply the input value by 6.

Step 2: Add *x* to this result.

Step 3: Divide this result by 4.

If an input of 7 to this function yields an output of 15, what is the value of *x*?

- A. 12
- B. 16
- C. 18
- D. 24

**Correct Answer:** C

**Explanation:**

**C**

**Advanced Mathematics (functions) MEDIUM-HARD**

Let the input number be 7.

Step 1: Multiply the input value by 6:

42

Step 2: Add *x* to that result:

42 + *x*

Step 3: Divide this result by 4:

This must yield an output of 15:

Multiply by 4:

60 = 42 + *x*

Subtract 42:

18 = *x*