Jane has a pre-paid cell phone with NextFell. 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 370 minutes and the cost was $133.00. In July she used 530 minutes and the cost was $181.00. A) Express the monthly cost C
C
in terms of x
x
, the number of minutes of calling time she used.
c

B) If Jane used 477 minutes of calling time in August, how much was her bill?
$

The monthly cost C =   $22 + $0.30x

Jane's bill for August is $165.10

The total amount Jane pays is the sum of the monthly fee and the charge per minute.

Total amount = monthly fee + charge per minute

Two equations can be derived from the question

a + 370b = 133 equation 1

a + 530b = 181 equation 2

Where:

a = monthly fee

b = charge per minute

This equation would be solved using simultaneous equation

Subtract equation 1 from equation 2

160b = 48

Divide both sides of the equation by 160

b = 48 / 160

b = 0.30

Substitute for b in equation 1

a + 370(0.30) = 133

a + 111 = 133

a = 133 - 111

a = 22

Based on the above calculations,  the monthly fee is $22 and the charge per minute is $0.30

Equation for monthly cost = $22 + $0.30x

If Jane used 477 minutes, total charge :

$22 + $0.30(477) =

22 + 143.10

= $165.10

A similar question was solved here: link

Step-by-step explanation:

A) Let x represent minutes used, and C represent monthly charge. We are given two (x, C) pairs: (370, 133.00) and (530, 181.00)

We can use these in the 2-point form of the equation for a line.

  y = (y2 -y1)/(x2 -x1)(x -x1) +y1

  C = (181 -133)/(530 -370)(x -370) +133

  C = 48/160(x -370) +133

  C = 0.30x -111 +133

  C = 0.30x +22

__

B) For x = 477 minutes, the charge will be ...

  C = 0.30(477) +22 = $165.10 . . . . for 477 minutes

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