Which equation represents the cost as a function of the number of washes ?

With an autoshine card , the total cost in dollars cbof your deluxe car washes is a linear function of the number of washes w . for 2 washes the cost is $50 . For $10 washes the cost is $90 ?

A)c=5w+40
B)c=5w+48
C)c=5w-248
D)c=5w-440

Think of it as having two ordered pairs. 2 washes for $50 can be thought of as the ordered pair (2, 50). 10 washes for $90 can be thought as (10, 90).

So, you are given two points on a coordinate plane. To find the equation of the line going through these two points, you need to first find the slope.

m = y2 - y1 / x2 - x1
= 90-50 / 10-2
= 40 / 8
= 5

So, the slope is m = 5. Now, use this with the point (2, 50) in the point slope formula. Then, solve for y.

y - y1 = m(x - x1)
y - 50 = 5(x - 2)
y - 50 = 5x - 10
y = 5x + 40

So, the answer is A

Use the info given and treat them as data points (2,50) and (10,90) and use y = mx + b where

m = change in y/change x = (90 - 50)/(10 - 2) = 40/8 = 5 so we get

y = 5x + b

choose one of the data points and plug into the equation and solve for b

50 + 5(2) + b

50 = 10 + b

40 = b

so we get

y = 5x + 40 so a