Answer:
11h 15 mins
Explanation:
This is because the difference between the two are basically you adding the higher number (20:30) then taking away the lower one (9:15). 20:30 - 9:15 = 11:15, since you are working out the difference, you have to convert it into hours and minutes, as they are the digits in the other two numbers, making the answer 11h 15m.