Answer:
C = 99 + 49m
x = $99
y = $49
Step-by-step explanation:
Let
x = one time joining fee
y = monthly payment
Your friend:
1 year = 12 months
x + 12y = $687
You:
x + 18y = $981
x + 12y = 687 (1)
x + 18y = 981 (2)
Subtract (1) from (2)
18y - 12y = 981 - 687
6y = 294
Divide both sides by 6
y = 294 /6
= 49
x = $49
Substitute y = 49 into
x + 12y = 687
x + 12(49) = 687
x + 588 = 687
x = 687 - 588
= 99
x = $99
C = 99 + 49m
Where,
C = total charges
m = number of months
99 = a one time joining fee
49 = charges per month