Question

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 100 minutes and the cost was $54.00. In July she used 660 minutes and the cost was $138.00.

Answer 1

Answer:

The costs of the plan are $0.15 per minute and a monthly fee of $39

Step-by-step explanation:

Let

x ----> the number of minutes used

y ----> is the total cost

step 1

Find the slope of the linear equation

The formula to calculate the slope between two points is equal to

$m=\frac{y2-y1}{x2-x1}$

we have the ordered pairs

(100,54) and (660, 138)

substitute

$m=\frac{138-54}{660-100}$

$m=\frac{84}{560}=\ 0.15\ per\ minute$

step 2

Find the equation of the line in point slope form

$y-y1=m(x-x1)$

we have

$m=0.15\\point\ (100,54)$

substitute

$y-54=0.15(x-100)$

step 3

Convert to slope intercept form

Isolate the variable y

$y-54=0.15x-15\\y=0.15x-15+54\\y=0.15x+39$

therefore

The costs of the plan are $0.15 per minute and a monthly fee of $39