Answer:
It will cost $42 for 28 binders
Step-by-step explanation:
We know that 15 binders = 22.50 dollars . We need to find the cost of 18, 30, 28, and 48 binders to figure out if they match up with the statements. One way to do this is to find the cost for one binder, and then multiply that by the number of binders to find the cost for a certain number of binders. For example, if one binder costs 2 dollars, five binders would cost 2 * 5 = 10 dollars.
To figure out how much one binder costs, we can use the division property of equality to divide both sides of our equation (15 binders = 22.50 dollars) by 15. We divide by 15 because anything divided by itself is equal to 1, and that would make it 1 binder = something dollars.
Applying this, we get
(15 binders)/15 = (22.5 dollars)/15
1 binder = 1.5 dollars
For 18 binders, this would cost 1.5 * 18 = 27 dollars. We know this because we add 1.5 dollars for each binder.
For 30 binders, this would cost 30*15=45 dollars
For 28 binders, this would cost 1.5 * 28 = 42 dollars
For 48 binders, this would cost 1.5*48 = 72 dollars
The only one that matches up is 28 binders for 42 dollars
and plug in r=4 and h=13 to get 
, so 
.