Answer:
Vince began practicing piano at 11:15 P.M
He stopped at 11:35 P.M
=> He practiced in 35 - 15 = 20 mins = 1/3 hour.
=> 1/3 hour means 1/3 circle, the number of degrees the minute hand turned:
N = (1/3) x 360 = 120 deg (1 circle = 360 deg)
Hope this helps!
:)