David is rowing a boat upstream. the river is flowing at a speed of 2 miles per hour. david starts rowing at a speed of 6 miles per hour, but as he gets tired his speed decreases (at a rate of 1 mile per hour, every hour). which equation represents the speed of the boat for x hours spent rowing?

Let v be Davids velocity...

v(t)=6-t

now he is rowing upstream so the velocity of the boat is decreased by the flowing river's rate of 2mph.  

Essentially the boat's velocity is a result of David's speed minus the speed of the river...

b(t)=v(t)-r  b=boat velocity, v=David's velocity, r=river velocity...

b(t)=6-t-2

b(t)=4-t  oh, sorry they want t to be x :)

b(x)=4-x

Best answer that i found on yahoo ok   set :   x= length of 2nd piece in cm  x- 3= length of 1st piece in cm  x-4= length of 3rd piece in cm  then since you know they all came from the 20 cm ribbon you add them together and set them equal to 20x+ x-3 +x-4 = 20  3x - 7= 20  3x= 27  x= 9  the shortest piece is the third piece which is x- 4  x-4  9-4 = 5  the length of the smallest piece is 5 cm.  the other lengths are  9 cm  6 cm