math
posted by Ryan .
A cell phone company offers a contract for which the cost C, in dollars, of T minutes of telephoning is given by C=0.25(t600)+71.95, where it is assumed the t greater than 600 minutes. What times will keep costs between $119.20 and $135.45?

$119.20 = 0.25(t600) + 71.95
$135.45 = 0.25(t600) + 71.95
Get rid of parenthesis and subtract 71.65 form both sides.
47.25 = .25t  150
Add 150 to both sides.
197.25 = .25t
Multiply both sides by 4.
789 = t
Do the same for the second equation.