<p>The speed of a swimmer is 4 km&nbsp;<span class="equation">\(h^{-2}\)</span>&nbsp;in still water. If the swimmer makes his strokes normal to the flow of river of width 1 km , he reaches a point 750m&nbsp; &nbsp;down the stream on the opposite bank.​​​​​​​ The speed of the river water is ___________ km&nbsp;<span class="equation">\(h^{-1}\)</span>​​​​​​​</p>