Simple javascript code

Hi,
I need to create a simple calculator that will calculate PSU efficiency savings.
This text will help you understand how the calculation is made:

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A PSU with 70% efficiency would have an input power of 100/0.7 = 143W
A PSU with 82% efficiency would have an input power of 100/0.82 = 122W
Power saving between the two is 21W. Let's assume that the PCs are in use for 10 hours a day (cost it makes our calculations simple!) - that's 210Wh or 0.21kWh saved per day. At 10p (pence is UK currency) per kWh, each PC equipped with a more efficient PSU saves 2p per day. You say you're in an educational environment, so 2p per day x 5 days per week x 39 weeks in a school year = £3.90 per year saved. Over the 5? year lifetime of the PC, that's £19.50.
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One kilowatt-hour is equal to 1,000 watt hours.