What the hel you expect us to do all that for 5 kids points? Go ask you mom to do that for you. If you're asking US to do that, then it has to be 40 or 50 points.
Answer: 12 3/8
10 1/2 + 10 1/2= 21
45 3/4 - 21 = 24 3/4
24 ÷ 2 = 12
Change the 3/4 into 8ths = 6/8
Divide that in half which gives you 3/8
So the length is 12 3/8
9/10 * 1000
which would give you 900