P_a and P_b Represent the Prices That Citizens (A)and (B),the

P_a and P_b represent the prices that citizens (a) and (b) ,the only two people in this nation,are willing to pay for additional units of a quantity (Q_c) of the public good.Q_s represents the quantity of the public good supplied by government at each of the collective prices. Refer to the above information.The collective willingness of this nation to pay for the fourth unit of the public good is:

A) $7.
B) $6.
C) $5.
D) $3.
For 4 units,Person (a) is willing to pay $2 and Person (b) is willing to pay $3,for a total of $5.