Step 1: Beta oxidation is a repeating four reaction sequence: oxidation, hydration, oxidation again, and thiolytic cleavage.
The final thiolysis step splits off a two carbon acetyl-CoA fragment from the fatty acyl-CoA chain.
Since only a two carbon unit leaves in each pass, a fatty acid with, say, 16 carbons needs seven full turns to be fully broken down. Answer: 2 carbons.