A. 80 < 100 + 82 + 70 + 72 + 80 + n < 90
80 < 100 + 82 + 70 + 72 + 80 + n < 90
6
80 < 404 + n < 90
6
6 * 80 < 6 * 404 + n < 6 * 90
6
480 < 404 + n < 540
480 - 404 < 404 + n - 404 < 540 - 404
76 < n < 136
CHECK - minimal - 76%. 100 + 82 + 70 + 72 + 80 + 76 / 6 = 80% (Sam's average).
B. Sam can get a B if he scores between 76, inclusive, and 136 exclusive, on his next test. So the minimal grade Sam can earn to earn a B in math is 76%.