If we call the time it took for you to climb the stairs in seconds, T, the height of the stairs in meters, h, your weight in newtons, W, then to find the power you developed in watts, P, the following formula restates what we said above:
Power = W x h/t, W= 71kg x 9.81m/sec sq.= 696.51 N, Height h= 3m, time t= 10 sec, Power P=( 696.51 x3) 10= 208.953 watts = 0.28 hp.