Word problems

Question

The phone company A Fee and Fee 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 420 minutes, the monthly cost will be $210. If the customer uses 860 minutes, the monthly cost will be $408.

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 A Fee and Fee plan.

Answer:
Do no use any commas in your answer.

B) Use your equation to find the total monthly cost if 931 minutes are used.
Answer: If 931 minutes are used, the total cost will be dollars.

Answer 1

Y=0.45x+21

0.45 =m=cost perminute

21=b=flat rate

420 min and 860 min are the x

408 and 210 are the y the cost

(X2,Y2)=(860,408) (X1,Y1)= (420, 210)

Y=mx+b.

M is the slope so to find it we can use m=(y2-y1)/(x2-x1) 

We were given 2 points in the question. Substituted into that slope formula and get (408-210)/(860-420)=0.45=m

 So the equation so far is y=0.45x+b

Now just substitute either one of the point into the equation and you can find b.

( 210=0.45(420)+b)

( 210=189+b)

Subtract 189 from both side

21=b

Check with the other point and you should have 21 as b as well. 

The full equation is y=0.45x+21.

Now substitute 931 into x and find y.