F(-1)= -3 is (-1,-3) and f(2) = 6 is (2,6) where f(x) = y
y=mx + b is the slope-intercept form whereas m equals the slope (rate of change) and b equals the y-intercept (initial amount/what y is when x is 0.)
First, we need to find the slope between the two points (-1,-3) and (2,6). To find the slope we could use one of it's formulas

.
1. (-1,-3)
2. (2,6)

→

→

The slope is 3 (

). Thusly, y = 3x + b
To find out the y-intercept, we can reverse the slope. [Note: This

is in

where rise is 'y' and run is 'x'. Reversed would be

]. Take the second ordered pair and use our reversed slope on it until we get 0 for x.
(2, 6) ⇒ (2 - 1, 6 -3) ⇒ (1, 3) ⇒ (0,0)
Y-intercept is 0. Therefore,
y= 3x + 0 [NOTE: y = f(x), so if you want it in function notation form it's just f(x) = 3x + 0.]
The cost is $45.50 for the bag
15; it represents the one-time sign-up fee
The y-intercept can be found either on the graph where the line intercepts the y-axis, or b in the equation y=mx+b.
It represents the fee because it will be charged even if the number of months (x) is zero. 10 is the monthly fee because it is multiplied by x, the number of months.
Step-by-step explanation:
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