Shelley was a key member of a close circle of visionary poets and writers that included Lord Byron; Leigh Hunt; Thomas Love Peacock; and his own second wife, Mary Shelley, the author of Frankenstein.
If the 900 watts means the input power, then 1000 w inverter would be ok. If the microwave produces 900 w of cooking power, you will need a bit more, maybe 1200-1400 w if you don't know what the input power rating of the microwave is.
Simply choose a bit smaller than the diameter of the screw that will be used to fasten the microwave oven up to the wall and drill at least the length of the screw into the wall stud. This will allow the screw to easily be placed in the wall. Continue to 6 of 8 below. of 08.