Ur independent variable is ur x values....ur dependent variable is ur y values..so if hrs are on the x axis, then ur independent values are ur hrs (or time)....and ur dependent values are ur distance.
y = mx + b slope(m) = 25 and since u have point (0,0), ur y int (b) = 0 so ur equation is y = 25x + 0 which is written as y = 25x...which is basically saying that he travels 25 miles per hr
how far will he travel in 24 hrs.....so sub in 24 for x y = 25(24) y = 600 miles
in summary : The dependent variable is distance, the equation is y = 25x and the dragonfly will fly 600 miles.