The elements of the set are numbers 17, 26, 35, 44, 53, 62, 71, 80

As

0+8 = 8 but putting 0 in tens place makes it single digit number so will not consider it.

8+0 = 80, number is 80

1+7 =8, number is 17

7+1 =8, number is 71

2+6 = 8, number is 26

6+2 = 8, number is 62

3+ 5 = 8, number is 35

5+3 = 8, number is 53

4+ 4 =8, number is 44

Set in roaster form is

C= {17, 26, 35, 44, 53, 62, 71, 80}