rowing a boat at a (constant speed) against the the current takes 7 hours to go 63 miles. with the current takes 9 hours. what is the speed of the current. thanks

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let the speed of the boat in still water be: x miles/hr       speed of current be: y miles/hrSo, v=dx/dt;x-y=63/7          ------ (1)x+y=63/9         ------ (2)Solve these equations simultaneously and find the answer.