The expression given for the salesperson's total earnings is
In this expression:
is a constant amount added to the earnings. represents the commission, which is 10% (or 0.1) of the sales amount .
Since the base salary is typically a fixed amount that the salesperson earns regardless of sales, and given that this fixed amount is added to the commission, we can conclude that:
A. his monthly base salary in dollars.
So, the correct answer is A.