The power in watts is the energy in Joules used per second. This is:
P [W] = E[J] / t[s]
Solving for Energy:
E = P*t
We must convert the time to seconds knowing that 1 min = 60 s:
t = 6 min × 60 = 360 s
Finally:
E = P*t
E = 133 W * 360 s
E = 47880 J
The work of the runner is 47880 J