A skateboarder rolls horizontally off the top of a staircase and lands at the bottom. The staircase has a horizontal length of   with a vertical drop of   . We can ignore air resistance. A grey staircase starts with the top upper left corner and ends with the bottom right corner of the diagram. A grey dashed arrow arcs downwards and points from the top of the stairs to the bottom of the stairs. Midway along the grey arrow is a skateboarder in the air above the staircase. A grey coordinate axis is shown at the right of the diagram with up and right indicated as the positive directions. What is the skater's initial horizontal velocity? Round your answer to three significant digits.