I don't fully understand this question as posted because I am not an Accountant or Economist or anybody who deals with accounting.

I will solve it as I understand the question. My understanding might not be correct, but this solution is still based on my understanding.

Four terms are mentioned: commission on Net sales, retuns, allowances, and gross sales.

Based on those, my understanding is

Net sale = (gross sale) minus (returns plus allowances)

So,

Net sales = (100 -8)% of Gross sales

Net = 92% of Gross ----***

$2036.88 = 11.25% of Net

2036.88 = 11.25% of (92% of Gross)

2036.88 = (0.1125)(0.92)Gross

Gross = (2036.88) / (0.1125)(0.92)

Gross = $19,680.00 ---------------answer.