John's dad gave him 8 3/4 pieces of wood. he used 4 2/3 pieces to make a bird house. his friend david then asked for 1 1/2 pieces. how much wood does john have left?

Ok so this all about subtracting fractions this is what you want to do:

you can change 8 3/4 and 4 2/3 to have the same value and deominator
8 3/4 = 8 9/12(multiply both sides by 3)
4 2/3 = 4 8/12(multiply both sides by 4)
you do this because 12 is divisible by 3 and 4

then, subtract 4 8/12 from 8 9/12 because John is using some of the wood his dad gave him.
then subtract once again, taking 11/2 away from your difference.
again match the deominator of 11/2 to the deominator of your difference which should be 12. another divisible of 12 is 2 and 6.
11/2 = 66/12 = 5 6/12(multiply both the top and bottom by 6)
and start subtracting.

so John should have -1 5/12(?) wood left

you’re answer is 8cm^3