Answer:
93
Step-by-step explanation:
The average is calculated as
average = [tex]\frac{sum}{count}[/tex]
On 3 quizzes
[tex]\frac{sum}{3}[/tex] = 73 ( multiply both sides by 3 )
sum = 219
On 4 quizzes, letting x be the score on fourth test
[tex]\frac{sum+x}{4}[/tex] = 78 ( multiply both sides by 4 )
sum + x = 312 , that is
219 + x = 312 ( subtract 219 from both sides )
x = 93
She must score 93 on the next quiz
