Anna's demand for snow boots is given by D(P) = 300-2P. Use this for the questions below. Q1. What is Anna's marginal benefit from purchasing the 20th pair of snow boots? Q2. What is Anna's total benefit from purchasing 20 pairs of snow boots? Q3. If the market price for snow boots where Anna lives is $120, how many pairs does Anna buy? Q4. If the market price for snow boots is $120, what is Anna's surplus from purchasing the snow boots?