Joel and bobby each move an identical box from the ground to a shelf that is 1.2m

Power = F * d / t
Joel = F * 1.2 / t
Bobby = F*1.2/(2*t)
J/B = F * 1.2/t // F * 1.2/(2t)
Invert the right fraction and multiply

J/B = [F * 1.2 / t] * [2t / ( F*1.2) ] Notice there is some cancellation that will take place.  The Fs are equal and so are the ts. The 1.2 will also go away.
J/B = 2/1

So written another way
Joel : Bobby :: 2:1 <<<< answer

3.4 is the max value of speed from curve and v axis