If the minute hand of a clock is 20 degrees behind the hour hand at this moment, then in 18 minutes, the minute hand will be how many degrees ahead of the hour hand?
The minute hand moves 2pi/60 = pi/30 rads every minute = 6° every minute
The hour hand moves pi/6 rads every hour so it moves pi/360 rads every miniute = .5° every minute
So...in 18 minutes....
The minute hand moves 18* 6 = 108°
And the hour hand moves .5 * 18 = 9°
The minute hand is 108 - ( 9 + 20) = 108 - 29 = 79° ahead of the hour hand after 18 mnutes