Question 287905
lettheir speed in still water be r

upstream their rate will be r-2

down stream their rate will be r+2

6/r-2 + 6/r+2 = 4

6(r+2)+6(r-2)= 4(r^2-4)

6r+12 +6r-12= 4r^2-16

4r^2-12r-16=0

4r^2-16r+4r-16=0

4r(r-4)+4(r-4)=0

(4r+4)(r-4)=0

so r=4 a positive number

they canoe at 4 mph in still water