Ax + c = R (subtract c from each side)
Ax + c - c = R - c
Ax = R - c (divide A from each side)
Ax/A = (R-c)/A
x = 
<-answer
Since the Power is directly proportional to the velocity, their ratio

is constant.
<span>Therefore </span>

which is a proportion:
500 : 1000 = x : 1728
that can be easily solved:
x = (500×1728)/1000 = 864kW
2x 2 - 6x = 0 .... if you mean 2x^2 - 6x = 0
then 2x = 0 and x - 3 = 0 << answer