This looks like a linear problem, where the answer desired takes the form of an equation such as y=mx+b.
'b' in this case is the initial cost, which could be zero, positive, or negative. On the graph it is the y-intercept. 'm' is the rate, as in the rise over run, but also the amount cost goes up or down by for each additional hour of rental.
The first sentence "A jet ski rental is $70 for two hours" tells us that after two hours (h=2), cost equals $70.00 (c=70). The second sentence tells us that after five hours (h=5), cost equals $130.00 (c=130).
These form two points on a Cartesian coordinate system, (2,70) & (5,130).
The simplest way to solve such a problem for slope (m) is to use 'Rise over Run':
(This formula finds the difference between the vertical elements ('Rise") and divides that ("over") the difference between the horizontal elements ("Run")
(Y2-Y1)
----------
(X2-X1)
Our two points come in X,Y pairs, (2,70) will be our (X1,Y1). (5,130) will be our X2, Y2).
Plugging in:
(130-70)
-----------
( 5 - 2 )
Simplifying:
60 / 3 which is 20.
So m = 20.
Plugging in the now known m, our assumed linear equation becomes (c)ost=20(h)ours-used+b (initial-cost), or c=20h + b.
The last thing to do is find b, the y-intercept, or initial cost at zero-hours.
There are some logic ways to finish this, and multiple math ways but let me lay out just two of the math ones.
First Math Method: Plug into Slope-Intercept
Using either point, lets just grab the first of (2,70), we can plug those values into the equation above.
c=20h+b becomes (70)=20(2)+b. Distribute to get 70=40+b, and solve to get b=30.
Now plug the b back into the same equation, and done: c=20h+30. The final answer in slope-intercept form.
Second Math Method: Use Point Slope Form
This is a tiny bit more elegant, and most math teachers like the traditional slop-intercept form but there is nothing wrong with others such as standard, or in this case, point-slope. A formula literally designed for situations like this. In flat Euclidean space there is only only line passing through a given point with a given slope, so its enough to say both the point and the slope. The formula goes something like this:
(Y-Y1)=m(X-X1). So we can simply drop in (c - 70 ) = 20 (h - 2) and be done. Final answer in point-slope form no extra work required like first method.
To verify this is the same answer, we could do some algebra.
Distribute the 20 to get Y - 70 = 20X - 40. Use equality properties to add 70 to each side. Now we are back at Y = 20X + 30, or the same with (h,c) instead of (x,y).
It may seem hard to learn when most get by with handy y=mx+b, but knowing the point-slope form makes solving lots of problems easier later on for the SAT, Trigonometry, and other classes, besides being required knowledge in many of them.
Best of luck and hope that was of some help!
