QUANTITIVE BUDGET ANALYSIS. KAPLAN QUESTION 160.

The management accountant of a business has identified the following information:

ACTIVITY LEVEL: 800units 1200units
TOTAL COST: $ 1640 $23600
The fixed cost of the business step up by 40% at 900 units.
what is the fixed cost at 1100units?
A) $6400 B) $7600 C) $10000(correct ans) D) $140000

I did the variable cost of $8 p.u correctly(as it was q159). at activity level above 900 the fixed cost step up by 40% therefore i feel 14000 is the correct answer. please help me understand why 10000 is the answer or is it printing error?

thanks.