Question

If 12 key chains cost $9, then 20 key chains cost $.......... .

Answer 1

12 Key chains divided by 9 Dollars is how much?
That will tell you how much each key chain costs individually!
So how much are 20 key chains?

Answer 2

Calculate the "price per key chain" form the the fact that 12 key chains cost $9

$9/12 key chains = $0.75/key chain

That^ will tell you how much each key chain costs individually!

Now 20 key chains will cost 20 times as much

$$\Huge 20•0.75$$

You should get an answer of $15.