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.