Luxottica Group, the Italian company that sells Ray Ban and Oakley sunglasses, reported net sales of 8.9 billion in 2018 and 9.2 billion in 2017. Gross profit decreased from 5.9 billion in 2017 to 5.7 billion in 2018 . Required: 1. Calculate the gross profit percentage for each year. (Round your answers to 1 decimal place.) 2. The change in gross profit was caused by: Complete this question by entering your answers in the tabs below. Calculate the gross profit percentage for each year. (Round your answers to 1 decimal place.)