Constant speed is 18mph. Went 40 miles up stream and 40 miles down stream. Total time was 4.5 hours. Was is the speed of the current.

Answer 1

current speed = 2 mph

distance = speed times time

upstream speed = 18-2 = 16 mph

upstream time = 2.5 hours. 40 miles = 16 x 2.5 = 40

downstream time = 4.5-2.5 = 2 hours. 40 miles = (18+2)(2) = 20(2) = 40

Answer 2

yay, found how Raymond says current=2

graph (18-x)*y=40,,,,same as y=40/(18-x)

graph (18+x)(4.5-y)=40,,,, same as y=[40/(18+x)]+4.5

notice the system is not linear, which makes linear algebra potentially not valid

see graphs meet at x=2 where x = current speed.

and where for both equations y=2.5. y=upstream time. 4.5 -y =downstream time