Refer to the following mentioned data. Net sales Cost of products sold Gross margin (In millions) 2017 2016 2015 $34,072 $30,530 $26, 191 14,672 13,332 13,220 $19,400 $17,198 $12,971 Required: a. Calculate the gross profit ratio for each of the past three years. (Round your answers to 2 decimal places.) 2017 % 2016 % 2015 % b. Assume that Campbell's net sales for the first four months of 2018 totaled $12.64 billion. Calculate an estimated cost of goods sold and gross profit for the four months, using the gross profit ratio for 2017. (Round intermediate calculations to 2 decimal places. Enter your answers in millions rounded to nearest whole number (i.e., 5,000,000 should be entered as 5).)