What is the slack time for activity H?

Project Sand Mandala
Carrie meticulously calculated the early and late start and finish times for her latest project and recorded them using different colors of sand on a pristine slab of white marble. She used red for late start and late finish times and green for early start and early finish times. Activity durations and their identifiers were written with black sand. She finished her task and had an opportunity to admire her work only briefly before a colleague came by and swept most of it away. Sadly, this was before Carrie could record the numbers on a more permanent medium, so now she turns to you to help.

Activity Predecessor Duration Early Start Early Finish Late Start Late Finish
A - 10
B - 7 11
C A 7
D A 15 14
E B 11 19
F B 10
G D,E 24
H F 24
J C 28
K G,H,J 36

A) 1
B) 2
C) 3
D) 4

Answer: D