The tax revenue will be , with determined by the intersection of the Inverse Demand Curve and the New Inverse Supply Curve, which is shifted upward from the original by .

Prior to the imposition of the excise tax, the equilibrium price . However, when the tax is implemented, demand will fall, thus you need to find:

You have Four Equations and Four Unknowns:

From the above, you can write , which has complex roots for Q. Thus it will not be possible to raise 300,000.

Perhaps you meant 300? If so, Q = 10 units or 15 units. Substituting Q=15 into the above yields , i.e