​ How much will Andrew earn over the course of 10 weeks?

Long way:

1st week=$4

2nd week=$17

3rd week=$30

.

.

.,

10th week=?

4th week=43

5th=56

6th=69

7th=82

8th=95

9th=108

\(\boxed{10th=121}\)

Thanks, tertre....If we want  the sum over all 10 weeks........

First week  =  $4

The common difference is 13

Last week  =  4 + 13(9)  =  $121

So....the sum is

[ First week + Last week ]  *   [ Number of weeks  ] / 2  =

[ 4 + 121 ] *  [ 10 ] / 2  =

125  [ 5 ]   =

$625