A cellular offers a contract for which the cost C, in dollars, of t minutes of telephoning is given by C=0.25 (t-600) + 41.95, where it is assumed that t ¡Ý 600 minutes. What times will keep costs between $79.95 and $117.20?
c-41.95 = (1/4)(t-600)
t-600 = 4 c - 167.80
t = 4c + 432.20
t = 4(79.95) + 432.2 = 752 min
t = 4(117.2) + 432.2 = 901 min