What is the reason behind the theory of why Denver and the high plains are so much higher then the surrounding area?

Because plates float on the Earth's mantle, parts of the Western United States might have risen, like an empty boat next to one with a heavy cargo, pushing the vast High Plains far above sea level, according to the theory formulated by geologists Craig Jones and Kevin Mahan at the University of Colorado-Boulder.

Explanation:

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1. (1.2kw)x(15/60hours) = .3kwh --> a

2. (5kw)x(90/60hours)x(8cents/kwh) = $0.60 --> d

3. microwave --> 1200 watts = (1.2kw)x(6/60hours) = .12kwh

coffee-maker --> 900 watts = (.9kw)x(10/60hours) = .15kwh

therefore, it requires more energy for the coffee-maker to do the same amount of work.

so the answer is a.