It means that he will be paid 100$ a week for his job. He gets additional money which is called commission if he sells products. He gets a percentage of the products that he sells. So since he sold 550$ of products and his commision is 6 percent. He will gain that amount addionatlly on top of hist 100$ base salary.
6% is .06, we have to multiply this by $550. .06 x 550 is 33$. So he will get, at the end of the week, 100$ PLUS his commission with is 33$ so a total of 133$.
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