I found a similar problem. This is its table:
Volunteering
Student Time(hours)
Amy 4 5/6
Beth 6 1/2
Victor 5 3/4
Cal 5 2/3
Match each pair of students with the difference between how much time they spent volunteering.
Amy and Victor : 11/12 HOURS
Amy: 4 5/6 → 29/6 ; Victor: 5 3/4 → 23/4
29/6 - 23/4 = 29/6(2/2) - 23/4(3/3) = 58/12 - 69/12 = -11/12
Cal and Beth : 5/6 HOURS
Cal : 5 2/3 → 17/3 ; Beth: 6 1/2 → 13/2
17/3 - 13/2 = 17/3(2/2) - 13/2(3/3) = 34/6 - 39/6 = -5/6
Beth and Victor : 3/4 HOURS
Beth: 6 1/2 → 13/2 ; Victor: 5 3/4 → 23/4
13/2 - 23/4 = 13/2(2/2) - 23/4(1/1) = 26/4 - 23/4 = 3/4