2002 seconds, or 33 minutes, 22 seconds.
First, let's calculate how many joules it will take to lift 78 kg against gravity for 1100 meters. So:
78 kg * 9.8 m/s^2 * 1100 m = 840840 kg*m^2/s^2
Now a watt is defined as kg*m^2/s^3, so a division of the required joules should give us a convenient value of seconds. So:
840840 kg*m^2/s^2 / 420 kg*m^2/s^3 = 2002 seconds.
And 2002 seconds is the same as 33 minutes, 22 seconds.
