For this case, the first thing we must do is define variables.
We have then:
x: number of minutes
y: total cost
We write the algebraic expression that models the problem.
We have then:

Simplifying we have:

Then, by the time the cost is equal to $ 300 we have:

From here, we clear the value of x.
Answer:
an algebraic expression for the problem is:

You can find the slope either by just looking at the line or using the slope formula.
#1: The slope formula is:
Find two points and plug it into the formula
I will use (0, 2) and (1, -1)
(0, 2) = (x₁, y₁)
(1, -1) = (x₂, y₂)

[two negatives cancel each other out and become positive]

m = -3
#2: To find the slope without having to do the work, you use this:

Rise is the number of units you go up(+) or down(-) from each point
Run is the number of units you go to the right from each point
If we start at a defined/obvious point, like (0, 2), find the next point and see how many units it goes up or down and to the right. The next point is (1, -1), so from each point, you go down 3 units and to the right 1 unit. So your slope is -3/1 or -3. You can make sure the slope is right by looking at another point.
Answer:
3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679
Step-by-step explanation:
The answer should be the 1st one.
Just use the quadratic formula and plug in the necessary numbers when requested and work from there.