Question

the phone company nextfell 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. if a customer uses 330 minutes, the monthly cost will be $57. if the customer uses 840 minutes, the monthly cost will be $108. a) find an equation in the form y = mx + b, where x is the number of monthly minutes used and y is the total monthly of the nextfell plan. answer: y = b) use your equation to find the total monthly cost if 978 minutes are used. answer: if 978 minutes are used, the total cost will be dollars. question help: video post to forum

Explanation:

Step1: Find the slope $m$

The two - point form of a line is given by $m=\frac{y_2 - y_1}{x_2 - x_1}$. Let $(x_1,y_1)=(330,57)$ and $(x_2,y_2)=(840,108)$. Then $m=\frac{108 - 57}{840 - 330}=\frac{51}{510}=0.1$.

Step2: Find the y - intercept $b$

We use the point - slope form $y - y_1=m(x - x_1)$ with the point $(x_1,y_1)=(330,57)$ and $m = 0.1$. So $y-57=0.1(x - 330)$. Expand to get $y-57=0.1x-33$. Then $y=0.1x + 24$.

Step3: Calculate the cost for 978 minutes

Substitute $x = 978$ into the equation $y=0.1x + 24$. So $y=0.1\times978+24=97.8 + 24=121.8$.

Answer:

A. $y = 0.1x+24$
B. If 978 minutes are used, the total cost will be 121.8 dollars.