put the on the same denominatior.

So it's 26 4/12 and 10 3/12.

Substract 10 3/12 from 26 4/12 (4/12 - 3/12 = 1/12)

You'll have 16 1/12 now divide it by 2 (because it's the total measurement that's free on the door (sorry if it's not clear...)).

Note: 2 is in reality 2/1

When you divide a fraction, you multiplie by the inverse.

So you keep the 1/12 and you multiply it by the invers of 2/1...1/2

1/12 * 1/2 = 1/24

Now add the 16 divide by 2 and you'll have you have your answer.

8 1/24