White would be 3/10. Since orange is 2/5, it can also be written as 4/10 since 4/10 simplified would be 2/5. Also since you know purple is 3/10, so you must add what you know to get what you don't know. Orange 4/10 plus purple 3/10 would be 7/10. You would then subtract what the whole thing is worth which is 10/10. 10/10 minus 7/10 would be 3/10 which is the remainder of what is left which is white.
A. Because you would have to find the common denominator, which in this case is 24. You would change 2 1/3 to 2 8/24, 1 1/8 to 1 3/24 and 1 3/4 to 1 18/24. Add these all up and you get 5 5/24.