Maria has taken three math tests and scored 78, 85, and 92. What score must she get on her fourth test to have an average score of exactly 86 for all four tests?

✓ Correct Answer: Option C

Let 'x' be the score on the fourth test. The average is (78 + 85 + 92 + x) / 4 = 86. Summing known scores gives (255 + x) / 4 = 86. Multiply by 4: 255 + x = 344. Subtract 255: x = 89.