You would need to make a 94 on the next quiz to have a mean quiz score of 90.
If 90 is the desired mean, then you have to multiply it by the number of quizzes
5 x 90 = 450 is the total in the 5 quizzes.
Now, add the scores of the first four quizzes.
88 + 95 + 93 + 80 = 356
Then, take the amount of the 5 quizzes and subtract it from the amount of the total 4 quizzes.
450 - 356 = 94