Dr. Seegert is an avid landscaper and gardener, resulting in the most beautiful house on his block. This increases property values on his street, resulting in a positive consumption externality for his neighbors. Below is a graph of the private and social benefit and private cost of Dr. Seegert's gardening. What is the new efficient quantity of gardening?

a = $6,385 b = $5,008 c = $4,897 d = $3,714 e = $2,584 f = $1,602