a celluar phone company offers a contract which the cost c, in dollars, of t minutes of telephoning is given by c=0.25(t-600) plus 57.95 where it is assumed that t is > or eqaul to 600 minutes. what time will keep cost below 102.45 and 135.20?

Answer 1

Assuming that your equation is correct:

102.45 ≥ 57.95 + .25(t-600)

Solve for t.

Do the same for $135.20.