In order to subtract fractions you need to have the SAME DENOMINATOR:
Let's say you have to subtract
3/2 - 4/5
As you can see, the denominators are different, therefore I need to use some math to make them equal. I will multiply the first fraction by 5 (top and bottom) and the second fraction by 2 (top and denominator)
I get:
3(5)/2(5) - 4(2)/5(2)
15/10 - 8/10
Now I have the same denominator (10) and I can subtract the top
(15 -8)= 7 and keep the same denominator.
My final answer is 7/10