Question 574818
C=0.25(t-600)+50.95, where it is assumed that t is greater then or equal to 600 minutes. What time keeps the cost between $97.95 and $123.45? 
-----------
97.95 <= 0.25(t-600)+50.95 <= 123.45
----
Subtract 50.95 along the line:
----
45 <= 0.25(t-600) <=72.50
---
Divide through by 0.25 to get:
180 <= t-600 <= 290
----
Add 600 along the line:
780 <= t <=890
==================
Cheers,
Stan H.
==================