A phone company has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone

Question

If a customer uses 390 minutes, the monthly cost will be $49.50. If the customer uses 780 minutes, the monthly cost will be $69.

1.  Find a linear equation for y, the monthly cost in dollars, of the cell plan as a function of x, the number of monthly minutes used.
2. Interpret the slope and y-intercept of the equation. 
3. Use your equation to find the total monthly cost if 678 minutes are used.

Answer 1

1. In order to find a linear equation you will need to use the slope intercept form y=mx+b.

To find slope m= (y₂-y₁₎/(x₂-x₁).

To find y-intercept b plug into the slope intercept form a given point and solve for b.

 

2. You will have to do this part on your own as it is an interpretation.

 

3. Using the equation we just found, plug in 678 to x and solve.