Of the 31000 total miles of railroad tracks in the US how many miles were in the North?

Of the 31000 total miles of railroad tracks in the US how many miles were in the North?
During the start-up of the Civil War to the ending of the conflictthe Union held a strategic and commanding advantage in terms ofquantity of rail lines. The Union held approximately 31,000-milescompared to Confederacy's 9,000. The advance and Confederatecaptures southward further increased the Union's rail capacity inthe North's favor.