-1 must be added.
15+(-6)+12=21. If you add one more number, then you would have to divide the sum by 4 to get the mean. 5*4=20. To get to 20, you have to add -1.
Answer:
16.2$
Step-by-step explanation:
Price of the notebooks: 15$
Tax Rate: 8%
Tax: 15$ * 8% = 1.2$
Price after Tax: 15$ + 1.2$ = 16.2$
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