an art instructor kept track of how many total pictures were painted by each of the people enrolled in her…

Explanation:

Step1: Count 'x's for 0 pictures

There are 5 'x's above 0, so 5 people painted 0 pictures.

Step2: Count 'x's for 1 picture

There are 0 'x's above 1, so 0 people painted 1 picture.

Step3: Count 'x's for 2 pictures

There is 1 'x' above 2, so 1 person painted 2 pictures.

Step4: Count 'x's for 3 pictures

There are 4 'x's above 3, so 4 people painted 3 pictures.

Step5: Count 'x's for 4 pictures

There are 8 'x's above 4, so 8 people painted 4 pictures.

Step6: Sum up the counts

$5 + 0+1 + 4+8=18$

Answer:

18