Suppose Dexter and Amy Are the Only Members of a Community

Suppose Dexter and Amy are the only members of a community that is trying to determine how much of the public good should be produced.Dexter's (inverse) demand curve is given by P = 50 - 5Q,while Amy's (inverse) demand curve is given by P = 150 - 15Q,where P is price or marginal benefit and Q is the quantity of the good.The marginal cost of producing the public good is constant at $80.Setting aggregate marginal benefit equal to marginal cost leads to the conclusion that the efficient quantity of the public good is equal to:

A) 2
B) 6
C) 10
D) 80.