(Advanced Analysis) the Equations for the Demand and Supply Curves

(Advanced analysis) The equations for the demand and supply curves for a particular product are P = 10 − 0.4Q and P = 2 + 0.4Q, where P is price and Q is quantity expressed in units of 100.After an excise tax is imposed on the product, the supply equation is P = 3 + 0.4Q.The equilibrium quantity before the excise tax is imposed is

A) 800 units.
B) 1,000 units.
C) 1,200 units.
D) 1,400 units.