Answer:
$15000.
Step-by-step explanation:
Given: Sales $90,000
Less Variable Exp (54,000)
Contribution margin 36,000
Less Fixed Exp (24,000)
Operating Profit $12,000
As sales decreases by 10%.
∴ Sales=

Sales=

Solving and opening the parenthesis.
Sales=

Sales= $81000.
Now, computing to get fixed expense at which operating profit will remain same.
Contribution margin= sales- variable expense
⇒ Contribution margin=

Fixed expense= Contribution margin - operating profit

∴ Fixed expense will $ 15000 at which operating profit will remain same.