The commission shall assess, adjust and equalize the aggregate valuation of the distributable property of each private car company. When the operations of any private car company extend into another state, the commission shall assess, equalize and adjust only such proportion of the total value of all the distributable property of such company as may be reasonably necessary to generate mileage in this state. The commission may require information in the forms required under sections 137.975 to 137.985 which may be necessary to properly assess and allocate such property.