okay, I used the power = change in energy/time equation and got this:
Ei = 510m
Ef = 13580.5m
Change in energy = 13070.5m
460000 = 13070.5m/140s
460000 = 93.4m
m = 4925.1kg
I'm not sure if this is right.
I started with calculating the Ep and Ek of the helicopter and got this:
Epi = 490m Eki= (1/2)(400m)
Epf = 12740m Ekf = (1/2)(1681m)
I don't really know where to go from there. Do the unknown mass variables cancel out? I'm lost!