Average: sum the quarters and divide by the number of quarters:
(60+80+75+x)/ 4 ≥ 70
Solve for x
(215+x)/ 4 ≥ 70
215+x ≥ 70 (4)
215+ x ≥ 280
x ≥ 280-215
x ≥ 65
3.4m questions
4.4m answers