$11.$ If a rail yard has $20$ parallel tracks, and each track is $400$ meters long, what is the total length of tracks in the yard?

$12.$ A high$-$speed train covers a distance of $500$ kilometers in $2$ hours and $30$ minutes. What is its average speed in meters per second?

$13.$ Calculate the wheelbase of a railway bogie if the distance between the centers of its wheels is $2\mathrm{.}5$ meters$\mathrm{.}\mathrm{}$

$14.$ If a freight train travels at a constant speed of $50$ miles per hour for $6$ hours, how far does it travel?$\mathrm{}$

$15.$ The track gauge of a narrow$-$gauge railway is $762$ millimeters. Convert this measurement to meters.