Let 'x' represent the number of days that Kaitlyn and Mark need to build the shed together, x>0.

Kaitlyn can build a shed in 6 days thus her rate is 1/6 shed per day.

Mark can build the same shed in 8 days thus his rate is 1/8 shed per day.

The together rate is 1/x shed per day.

1/6 + 1/8 = 1/x

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x = 24/7 days

x = 3 days (3/7)24 hr

x = 3 days 10 hr

Kaitlyn and Mark will need 3 days and 10 hours to build the shed together.