Water flows in a river. At $9$:$00$ AM the flow past bridge #$1$ is $2000$ cfs $(55$ m$3/$s$).$ At the same instant, the flow past bridge #$2$ is $1600$ cfs $(45$ m$3/$s$).$ At what rate is water being stored in the river between the two bridges at this instant. Assume zero seepage and negligible evaporation.