It is given in the question that
Sam sells cars and earns 3.5% commission in sales. In one day he sold 3 of the same cars each for $21,500.
Selling price of each car is $ 21,500. Therefore selling price of 3 cars is

And Sam earns 3.5 % commission .
So to find the Sam's commission, we have to do

And the Sam's earning is $2257.50 .