Question 344841
(77+72+85+x)/4=80
(234+x)/4=80
234+x=4*80
234x=320
x=320-234
x=86 is the lowest score for a B.
(77+72+85+100)/4=x
334/4=x
334=4x
334/4=x
83.5=x 
The max score of 100 gives an average of 83.5.
Range is 86 to 100.