A cellular phone company offers a contract for which C, in dollars of t minutes of telephone is given by

C= 0.25(t-400) + 48.95

Assuming that t > 400

What times will keep (for the cost) between $90.70 and $129.95

Phone time must be between ________ Min and _______ Min.

What do I have to do first? Estimate the amount of minutes?