Find the speed of a boat both upstream and downstream if the speed of the boat in still water is 21mph and the speed of the current is 9mph

For upstream: 12 mph

For downstream: 30 mph

Step-by-step explanation:

Given that the speed of the boat in still water is 21mph and the speed of the current is 9mph

To find the speed of a boat both upstream and downstream,

For upstream, the boat is moving against the direction of the current. The speed will be:

21 - 9 = 12 mph

For downstream, the boat is moving toward the current direction. The two speed will be added together. That is,

21 + 9 = 30 mph

If the direction of the both is perpendicular to the direction of the current, then we will use pythagorean theorem

Speed = sqrt( 21^2 + 9^2 )

Speed = sqrt( 522 )

Speed = 22.85 mph

if you was gonna solve for a, a is a   < -12