First change them to improper fractions
3 3/5 + y + 5 2/3 = 15
3 3/5 = 18/5
5 2/3 = 17/3
now find the common denominator which would be 3 × 5 = 15
18/5 = 54/15
17/3 = 85/15
now add
(54 + 85) = 139/15
now divide
139 ÷ 15 = 9 4/15
now we need to find the missing factor
15 is our total, so now we have to subtract
15 - 9 4/15
change to improper fractions
15/1 − 139/15=
((15 × 15) − (139 × 1)) / (1 × 15) =
(225 - 139) / 15=
86/15
now divide
86 ÷ 15 = 5 11/15
Your answer is B. 5 11/15
Hope this helps. :)