Please, explaine step by step with formulas. thank you!

Understanding income statement relationships-Apple Inc. Selected data from the September 30,2017, and September 24, 2016, consolidated balance sheets Problem/2. and income statements for the years then ended for Apple Inc. follow. All amounts are LO 2, 4 reported in millions. Gross profit - Operating Expences Required: a. Calculate the amount of Apple's gross profit for each year. Has gross profit as a percentage of sales changed significantly during the past year? b. Calculate the amount of Apple's operating income for each year. Has operating income as a percentage of sales changed significantly during the past year? c. After completing parts a and b, calculate the other missing amounts for each year