Please help, this confuses me.

Exercise 13-3 Computing and interpreting common-size percents LO P1 Sales Cost of goods sold Accounts receivable 2019 2018 2017 $ 453,474 $ 292,564 $ 237,857 $ 229,287 147,932 122,179 22,039 17,144 16,341 2016 2015 174,895 $ 131,500 88,448 65,750 10,231 8,981 Compute trend percents for the above accounts, using 2015 as the base year. Trend Percent for Net Sales: 1 Choose Denominator: 7 Base year net sales Trend percent 0 % Choose Numerator: Analysis period net sales 2019: 2018: 2017: 2016: 0 % 0 % 0 % Trend Percent for Cost of Goods Sold: 1 Choose Denominator: / Base year net sales Choose Numerator: Analysis period net sales 2019: 2018: 2017: 2016: Trend percent 0 % 0 % 0 % 0 % Trend Percent for Accounts Receivables: 1 Choose Denominator: 1 Base year net sales Trend percent 0 % Choose Numerator: Analysis period net sales 2019: 2018: 2017: 2016: 0 %