Me with the whole page. i need the answers and calculations !

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

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

the answer would be c ≈ 18.852*3.14= 6.286.28*3=18.85