Amber plays video games five nights a week and her current grade in engineering is 70 percent. She decides to play video games for six nights each week and her engineering grade falls to 50 percent. What is Amber's marginal cost of playing video games one more night each week? Amber's marginal cost of playing video games one more night each week is A. 70 percentage points B. greater than 50 percentage points and less than 70 percentage points C. 20 percentage points D. 50 percentage points