if you are asking "what is 3 and 1/2 as a mixed number", the answer is that it already is in mixed number format.
It is: 2 and a 1/2 as a mixed number
17.5 as a mixed number equals: 17 5/10 = 17 1/2
it would be 2 1/2, which is 5/2 as a mixed number.
21/2 is itself a mixed number
The mixed number is 32 1/2
2/3+2/5 as a mixed number is 1 and 1/15
8 1/2
21.5 as a mixed number = 21 1/2
15.50 as a mixed number = 15 1/2
The mixed number of 3.50 is: 3 1/2
The mixed number is 14 1/2