Ellen has three exam scores 82, 74, and 90. What score on her next exam will give her an average of 85 over the four exams?

Let $x$ be the next score. The average condition is $(82 + 74 + 90 + x)/4 = 85$. The numerator simplifies to $246 + x$, so $246 + x = 340$, giving $x = 94$. Substituting back, the four scores total 340 and divide by 4 to give 85.