Answer:
One-sixth d + one-eighth d = 1
Explanation:
When they work together, their rates of completion add. They want to build one shed, so the number of sheds being built is ...
(Kaitlyn's sheds per day)×(days Kaitlyn works) +(Mark's sheds per day)×(days Mark works) = 1 shed
(1/6)d + (1/8)d = 1 . . . . matches the last choice