Four consumers, A, B, C, and D, are each willing to pay $9, $8, $7, and $6, respectively, to buy one unit of some good. Four producers, E, F, G, and H, are each able to produce one unit of that good at a cost of $3, $4, $5, and $6, respectively. At a price of $6, what is the combined total of consumer surplus and producer surplus in this market?

a.$8b.$9c.$10d.$11e.$12