You have a 20-ounce bottle of juice. you pour out 14 of the bottle to share with a friend. if you pour out 3 ounces for yourself, what fraction of the 20 ounces will be left in the bottle?

As you can see in the question, this deals with fractions. So that's what you're going to want to use to solve it. Start with a fractoin for the whole bottle:
whole=20/20
It's a twenty ounce bottle, so your denominator is twenty.
There are twenty ounces in the bottle, making your numerator twenty.

Now, you give your friend fourteen ounces out of a twenty ounce bottle. That looks like this:
friend=14/20
It's a twenty ounce bottle, so your denominator is twenty.
Your friend took fourteen ounces, making your numerator fourteen.

Now, you take three ounces yourself. That looks like this:
you=3/20
It's a twenty ounce bottle, so your denominator is twenty.
You took three ounces, making your numerator three.

Now to find your answer, how much is left. This is your equation:
leftover=whole-friend-you
You do this because you need to take away the juice you and your friend took from the original bottle. So you start with the whole, take away what your friend took, then take away the juice you took. That will look like this:
leftover=20/20-14/20-3/20

When subtracting fractions, you first make all the denominators the same. In this convenient problem, that's already done for you. Next, you subtract the numerators:
20-14-3=3

And put your result over your common denominator, twenty:

leftover=3/20
And there's your answer.