Recall your d = rt, distance = rate * time.
b = speed rate of the boat.
c = speed rate of the current.
keeping in mind that, as the boat goes Upstream, against the current, it's speed is not "b", but is really " b - c ", because the current is subtracting speed from it.
likewise, when the boat is going Downstream, because is going with the current, is really going faster at " b + c ".
what is the speed of the boat? well, 61 + c = b.
b = speed rate of the boat.
c = speed rate of the current.
keeping in mind that, as the boat goes Upstream, against the current, it's speed is not "b", but is really " b - c ", because the current is subtracting speed from it.
likewise, when the boat is going Downstream, because is going with the current, is really going faster at " b + c ".
what is the speed of the boat? well, 61 + c = b.