Question 9420
Your not considering your signs when you do your addtion and subtraction.

{{{18/24-(-14/24)-21/24}}}

When you subtract a negative number it is the same as adding it, so:

{{{18/24-(-14/24)=32/24-21/24=11/24}}}

watch your signs, it can get tricky when you go to fast.  Remember when subtacting a negative number you add it.