Suppose Residents of Toadhop Live on the Quabache River,a River

Suppose residents of Toadhop live on the Quabache River,a river prone to flooding.Suppose there are 1000 (type A) people who value flood control more than the 1000 (type B) people. Type A Demand Q_D = 100 - P
Type B Demand Q_D = 50 - P
Where Q measures the quality of flood control.If the price of a unit of flood control is $100,000 and the citizens of Toadhop gather for a townhall meeting to find the socially optimal level of flood control,and they are successful,how much will type B individuals contribute per unit of flood control?

A) 25
B) 50
C) 75
D) 100