I Don't know the Formula to use or how to get the percentage.

The income statements of Ivanhoe Corporation show the following amounts: 2020 $740 520 2019 $710 493 2018 $660 435 Net sales Cost of goods sold Gross profit Selling, general, and administrative expenses Profit before tax 220 217 225 190 145 107 30 72 118 Using vertical (common-size) analysis, analyze Ivanhoe Corporation's declining profit before tax. (Round answers to decimal places, eg. 52%.) 2020 2019 2018 Net sales % % Cost of goods sold % % % % % % Gross profit Selling, general, and administrative expenses Profit before tax % % % % % %