Question 546324
Let
Her score for forth exam = x


Given
Average Score for 3 exams = 84
Total score for 3 exams = 84*3=252
Total exams = 4
Average = 85 (for four exams)


sum of quantities / number of quantities = Average


(252+x)/4= 85
252+x=85*4
252+x=340
x=340-252
x=88

She must score 88 to get an average of 85.