Puzzle ZIPI 

Workings

Hint
A baker's dozen is usually 13.

Answer
Hours in a week.

Reasoning
A dozen is 12, but a baker's dozen is usually 13.

So a dozen (12) baker's dozen (13) = 12 x 13 = 156.

There are 24 hours in a day, and 7 days in a week.

So there are 24 x 7 hours in a week = 168.