Math problem help, current speed

Julie and Robert row their boat at constant speed 63miles downstream for 7 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 9 hours. Find the rate of the current.

I just want to know how to set up the problem, why do it that was and how to solve it.

As we all know,

D=ST;
where d = distance
S = speed
T = time.

Based on the problem, we can conclude that:

Ddownstream = Dupstream.

So:
(Sboat + Scurrent)(timedownstream) =63miles
(Sb + Sc)7 = 63

(Sboat - Scurrent)(timeupstream) = 63miles
(Sb - Sc)(9) = 63

Solving algebraically you will get:
Sb = 8mph
Sc = 1mph

Goodluck:)

While rowing downstream, a boat's speed is equal to (boat's original rowing speed + current speed) due to the support of the current.
While rowing upstream, a boat's speed is equal to (boat's original rowing speed - current speed) due to the opposition of the current.

Let the original rowing speed of boat be 'b' miles per hour and the speed of the current be 'c' miles per hour.

Boat travels 63 miles in 7 hours while traveling downstream.

Boat's net speed while traveling downstream = 63 miles / 7 hours = 9 mph.
=> Boats original rowing speed + current's speed = 9 mph
=> (b + c) mph = 9 mph
=> b + c = 9 ---(equation 1)

Boat travels 63 miles in 9 hours while traveling upstream.

Boat's net speed while traveling upstream = 63 miles / 9 hours = 7 mph.
=> Boats original rowing speed - current's speed = 7 mph
=> (b - c) mph = 7 mph
=> b - c = 7 ---(equation 2)

Adding equation 1 and 2,

( b + c ) + ( b - c ) = 9 + 7
=> 2b = 16
=> b = 8

Putting b = 8 in equation 1, we'll get
8 + c = 9
=> c = 1

Hence, the speed of current is 1 miles per hour.

Let the speed of rowing = u mi/hr