Slope-intercept form:
y = mx + b
"m" is the slope, "b" is the y-intercept (the y value when x = 0) or (0,y)
To find "m", you use the slope formula and plug in two points:
I will use (0, 20) and (2, 80)
(0, 20) = (x₁ , y₁)
(2, 80) = (x₂ , y₂)
[tex]m=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}[/tex]
[tex]m=\frac{80-20}{2-0}[/tex]
[tex]m=\frac{60}{2}[/tex]
m = 30
y = 30x + b
To find "b", you can plug in a point into the equation, or you can look at the graph and find the y value when x = 0.
When x = 0, y is 20, so the y-intercept is 20
y = 30x + 20 The 3rd option is your answer
You could have also just used the information they gave in the beginning and make an equation:
x = the number of days
y = total cost
y = 30x + 20 [$30 per day plus a one time fee of $20]
