Math Help Needed!!! Again!!!!

[mlwilliamsiv]

Last one...I just don't wanna get this one wrong...

Here is the problem:

Suppose that the monthly cost of a long-distance phone plan (in dollars) is a linear function of the total calling time (in minutes).

The monthly cost for 41 minutes of calls is $12.48. The monthly cost for 75 minutes of calls is $15.54.

What is the monthly cost for 48 minutes of calls?

I need to try to figure out the slope I guess...I thought it was 0.09 cents a minutes trying to figure out the difference between the two monthly totals above but that was obviously wrong. I'm done problems like this before with the slope given but I'm having trouble with this one.

Any help will be greatly appreciated.

THANKS!