Answer :
Answer:
Socially optimal quantity of security is 18 hours.
Explanation:
Marginal Benefit & Marginal Cost are additional benefit, cost while producing/ buying an additional unit of a commodity.
Social optimality is where Marginal Benefit = Marginal Cost
Marginal Demand/Benefit Curve (for 1 house) : p = 20 - q
Marginal Demand/Benefit Curve (15 houses) : 15 x Individual MR 15 [p = 20-q]. So, 15p = 300 - 15q
As Social optimality is at Marginal Benefit , Marginal Cost Equality.
MC = P = 30 {Given}
300 - 15q = 30
300 - 30 = 15q
270 = 15q
q = 270/15 = 18