With math homework. i'll mark you as brainiest!

For the living room one, you have an 11' wall, & a 2' 6" shelf.
First, we'll divide the length of both in half:
5' 6" wall, 1' 3" shelf
Now, subtract the two:
4' 3"
That's how far away the edge of the shelf needs to be from either corner of the wall to be centered.

For the second one:
We need to get all these numbers into the same formatting. I say we go fraction.
First guy got 13 out of 18
Second guy got .7 (repeating)
Third guy got 5/6
Ok, first, we'll turn .7 repeating into a fraction. This won't always work, because not all decimals will turn into a nice fraction. But this one will.
.7 (repeating) = 7/9
So we have:
13/18
7/9
5/6
Now, we can't compare these quite yet. They all need to have the same denominator. So, what's the LCM of the three denominators? 18, right?
The first one can be left alone, since it has a denominator of 18 already. The second one: multiply both numbers by 2, and we get 14/18. For the third: multiply everything by 3, and we get 15/18.
NOW let's compare them:
Jon: 13/18
Jim: 14/18
Joe: 15/18
It's now clear that Joe got the highest score.

270 books in each shelves