The plaintiff railway, doing local and interstate business, brought suit to recover payment made under a state net income tax measured by the difference between gross operating revenues for the whole business proportioned by the ratio of track mileage within and outside the state and operating expenses similarly proportioned. Held, such a formula for taxing the local income of a concern doing both intrastate and interstate business was not on its face invalid and the mere showing that the plaintiff's local costs were higher than the system average without also showing that intrastate revenues were not correspondingly greater did not sustain the plaintiff's burden of proving the tax unreasonable. Norfolk & W. Ry. v. State of North Carolina ex rel. Maxwell, (U.S. 1936) 56 S. Ct. 625.