Absorption and Marginal costing

Sir I found a question in the study text and I am confused by this

It gave the format for the absorption costing statement and I needed to find the under/over absorption of overheads

When I was trying to find it I noticed that they haven’t used he correct equation I think and have used actual fixed production costs-standard fixed production costs

I thought that when finding overhead costs that we need to deduct standard fixed production overhead cost from actual fixed production costs

Sir this was the data that was given
$

Fixed production overhead. 5

The fixed production overhead figure has been calculated on the basis of a budgeted normal output of 36000 units per annum. The fixed production overhead incurred in March was $15,000

No of units produced
Produced 2000 units

Sir in this question did they use
Standard fixed production overhead cost- Budgeted fixed production overhead cost because they haven’t given the actual figures

Is that the reason they have calculate under absorption like this?