To convert the speed from kilometers per hour to miles per hour, you can use the conversion ratio of 1 kilometer = 0.62 miles.
To find the speed in miles per hour, you can multiply the speed in kilometers per hour by the conversion factor:
\[ 900 \text{ km/h} \times 0.62 \text{ miles/km} = 558 \text{ miles/h} \]
So the speed of the airplane in miles per hour is 558 miles/h.
Since this answer is not one of the provided options, there may be a mistake in the options or in the interpretation of the exercise. Please double-check the problem context or the provided responses.