The Following Items Were Taken from the Financial Statements of Henager

The following items were taken from the financial statements of Henager Inc. over a three-year period: $\begin{array}{lccc}\underline{\text { Item }}&\underline{2017}&\underline{2016}&\underline{2015}\\\\text { Net Sales }&\$355,000&\$340,000&\$300,000 \\\text { Cost of Goods Sold } &\underline{214,000}&\underline{202,000}&\underline{186,000}\\\text { Gross Profit } &\underline{\$ 141,000} &\underline{\$138,000}&\underline{\$114,000}\\\end{array}$ Instructions
Compute the following for each of the above time periods.
a. The amount and percentage change from 2015 to 2016.
b. The amount and percentage change from 2016 to 2017.