The economic staff of the US Department of the Treasury has been asked to recommend a new tax policy concerning the treatment of the foreign earnings of US firms. Currently the foreign earnings of U.S. multinational companies are taxed only when the income is returned to the United States. Taxes are deferred if the income is reinvested abroad. The department seeks a tax rate that will maximize total tax revenue from foreign earnings. Find the optimal tax rate if
a. B(t) = 80 − 100t
b. B(t) = 80 − 240t2
c. B(t) = 80 − 801t, where B(t) is the foreign earnings of US multinational companies returned to the United States and t is the tax rate.