Word problem question

Question

Suppose a student has earned the following grades on her first four quizzes: 83, 72, 89, 78. What must she score on her fifth quiz in order to have a mean of 80 on all of her quizzes?

Answer 1

(x + 83 + 72 + 89 + 78)/5 = 80

x + 322 = 80*5

x = 400 - 322

x = 78

Answer 2

after withdrawing $58, mark had $200 left in his savings account. how much money was in the account before the withdrawl?