The answer for the 69 is B and 70 is C

I don't know why. I need an explanation.

Use the information below to answer the next two questions: Firms A and B are two identical firms in a Cournot Duopoly. If the market demand in this industry is given by: P = 100 -(1/2) Q and marginal cost: MC = 50. 69) Firm A would produce zero quantity of this product if firm B were to produce a) 50 units. b) 100 units. c ) 0 units. d) 33.33 units. 70) The best response equilibrium in this Cournot duopoly is for firms A and B to produce quantities respectively. a) 50 and 50 b) 100 and 100 c) 33.33 and 33.33 d) 50 and 33.33