Flexing budget

Hello sir,

While attempting this question I valued fixed cost on the basis of 13,600 Units. but my answer was incorrect, they have valued fixed overhead on the basis of 15000 unit.

It is different from what i have seen in your lectures.
Can you please explain.

F Ltd makes a single product for which the budgeted costs and activity for a typical month
are as follows:
Budgeted production and sales 15,000 units
Budgeted unit costs $
Direct materials 30
Direct labour 46
Variable overheads 24
Fixed overheads 80
––––
180
––––
The standard selling price of the product is $220 per unit. During October only 13,600 units
were produced.
What is the total budget cost allowance contained in the flexed budget for October?

Thank you in advance