So they tell us that minimum r is 100. So basically you have $100 for the first 4 hours and then (.2*100 = $20) for each additional hour.
(1) Tells us the total charge was $288.

Hmmm.. How do we get from $100 to $288? Well, the first $100 is 4 hours. So how many additional hours at $20/addl hour would it take to get to $288?

Well, you need 5 additional hours to get to $200. To get to $288, you would need a little more than 9 additional hours—on top of the original 4 hours.
Combined, you get at least 13 hours.

Now ask yourself—did the job take more than 10 hours? YES!

Now you should notice there is a variable r in the question. Can you think of another value for r such that the answer to the question is NO, instead of YES?

Well, you are told the minimum r is 100–however, there is no maximum for r! So what if r were $288. So it costs $288 for the first 4 hours?
Well, it looks like (1) is satisfied and the number of hours is only 4 hours!
Going back to the question—did the job take more than 10 hours? NO!

So clearly we have conflicting answers here–YES and NO. Therefore, you know (1) is no good–so the answer must be (B), (C), or (E).

Now let’s look at (2):
A total of 2.4r dollars. Well, we know minimum r =100—so 2.4r would be $240.
How many hours to get to $240? Well, $100 for the first 4 hours means there’s $140 left to go from $100 to $240. $140 divided by $20/additional hour means 7 extra hours.

Add that 7 hours to the original 4 hours and you get 11 hours. Is that more than 10 hours? Yes!

What if r were a higher number? What if r=1,000? So the total job costs $2,400. With $1,000 for first 4 hours + $200 per additional hour—that would be a total of 4 + 7 additional hours = 11 total hours.
Is that more than 10 hours? YES! So you see it doesn’t matter what r is—the answer here is always YES.