prep的数学题，帮忙解答一下，关于sales tax

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At a certain restaurant, if each hamburger costs the same amount, what is the cost, excluding sales tax, of 1 hamburger?

(1)  The total cost, including a 6 percent sales tax, is $4.77 for 3 hamburgers.

(2)  The total cost, including a 6 percent sales tax, is less than $6.50 for 4 hamburgers.

总能遇到sales tax 的题，sales tax是怎么收的呢？是在price上乘税率，还是在成本上呢？求求nn们帮忙解答一下