Jeannie's scores on her first four tests were 80, 65, 87, and 75. what will
she have to score on her next test to obtain an average of at least 80 for the term?

She will have to score 93.
(80+65+87+75+x)/5 = 80
307+x = 400
x =400-307=93
Another way, easier to do in your head:
Notice that 65 is 15 below 80, 87 is 7 above 80, and 75 is 5 below 80. The overall situation is 13 below 80 (because -15+7-5=-13). For a number to push the average back to 80, it must be 13 higher than 80. 80+13=93

We need the pictures of the graphs