The formula for calculating power is expressed as
Power = work done/time
work done = force x distance
Recall, force = mg
where
m is the mass
g is the acceleration due to gravity
From the information given,
m = 135 lb
g = 9.81 m/s^2
distance = 5.6
time = 4.5 s
We would convert 135 lb to kg
Recall,
1 lb = 0.4536 kg
135 lb = 135 x 0.4536 = 61.236 kg
Force = 61.236 x 9.81 = 600.72516 N
work done against gravity = 600.72516 x 5.6 = 3364.060896
Power = 3364.060896/4.5
Power = 747.57 W