Lee, as a consumer, places the value on a unit of chemical product as follows.

Value of first unit: $30 Value of second unit: $28 Value of third unit: $26 Value of fourth unit: $24 Value of fifth unit: $21 Value of sixth unit: $19 Value of seventh unit: $17

Ernie, as a producer, pays the following cost to produce the chemical product.

Cost of first unit: $12 Cost of second unit: $15 Cost of third unit: $17 Cost of fourth unit: $19 Cost of fifth unit: $21 Cost of sixth unit: $24 Cost of seventh unit: $26

Using the information given above, derive the size of producer surplus at the equilibrium price.

(1) 24 (2) 21 (3) 18 (4) 15