Edgar is getting better at math. on his first quiz he scored 57 points then he scores 61 and 65 on his next two quizzes if his scores continued to increase at the same rate what will be his score on his 9th quiz?

a- write and explicit formula for the sequence. explain where you found the numbers you are putting in the number formula

First, we need to determine if the sequence is an arithmetic or a geometric. So the arithmetic sequence is referred to a sequence that the difference between the numbers is constant. While the geometric sequence is a sequence where each number after the first is identified by multiplying the previous one by a fixed number. 

 Given 
  57, 61, 65   the difference between the numbers is 4

Solution
Arithmetic sequence
An= 65+4     An= 69+4    An= 73+4    An= 77+4     An= 81+4     An= 85+4
An= 69         An= 73         An= 77        An= 81          An=  85       An= 89  

The score of Edgar for his 9th quiz is 89 points.