For this clock: Power = (120 volts) x (0.5 ampere) = 60 watts .
Note: 60 watts is the correct solution when you use the given information. But 60 watts is a totally ridiculous power consumption for an electric alarm clock. 2 to 5 watts would be reasonable ... maybe 15 to 25 watts if it's part of a fancy clock+radio+telephone+night-light set.