Webassign due in like half hour i have the problem down but its not working

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webassign due in like half hour! i have the problem down...but its not working!

Homework Statement



A steam iron draws 8.0 A when connected to a potential difference of 120 V.
(a) What is the power rating of this iron? 960 W <<<<correct

(b) How many joules of energy are produced in 20.0 min?
320 J <<<incorrect why?

(c) How much does it cost to run the iron for 20.0 min at $0.010/kW·h?
.0032 $ <<<<correct


Homework Equations



for part b: 960*(20/60) = 320

whys it wrong?!
 
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One Watt = one Joule per second. You need to multiply the power (960 W) by the time in seconds (not hours).