2. The following table shows how the marginal benefit of service varies for four consumers

Marginal Benefits of Consumers
QuantityNabeela      Misbah    Summiya    Arzoo
1          1000              800          600           400
2           800               600         400            200
3           600               400         200            100
4           400               200         100              50

Suppose the service is pure private good and is sold in a competitive market with the only buyers being the four people whose marginal benefits are shown in the table. If the market price of the product is $400, what is the quantity demanded?