4: (3/4 - 1/2) X 3/5.
You need them all to have the same denominator (bottom number)
The lowest common denominator (LCM) of 2,4 and 5 is 20
4 X 5 = 20
2 X 10 = 20
5 X 4 = 20
Then multiply the top number by the amount you need to multiply the bottom number by to get 20
3 X 5 = 15
1 X 10 = 10
3 X 4 = 12
(3/4 - 1/2) X 3/5. Turns to (15/20 - 10/20) X 12/20.
15 - 10 = 5
5 X 12 = 60
Answer: 60/20
Simplified: Either 3 or 3/1.
If you use the steps above then you should be able to do the rest :D
If you need anymore help, please ask