Question 1200356
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Jane has a pre-paid cell phone with Splint. She can't remember the exact costs, but her plan has a monthly fee 
and a charge for each minute of calling time. 
In June she used 130 minutes and the cost was $76.50. 
In July she used 510 minutes and the cost was $209.50.
A) Express the monthly cost as C as a function of X, the number of minutes of calling time she used.

B) If Jane used 205 minutes of calling time in August, how much was her bill?
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<pre>
The difference in the cost, 209.50 - 76.50 = 133 dollars, is due to the difference of minutes

    510 - 130 = 380 minutes.


Hence, each minute costs  {{{133/380}}} = 0.35 dollars.


Now we can compute the monthly fee.  It is  76.50 - 130*0.35 = 31.00  dollars,
from the June's bill.


Hence, the cost function is  C(X) = 31 + 0.35*X.


It is your <U>ANSWER</U> to question (A).


To answer question (B), you should calculate

    C(205) = 31 + 0.35*205 = 102.75 dollars.


It is the <U>ANSWER</U>  to question (B).
</pre>

Solved.