If the golf ball has horizontal velocity of 5.5 m/s and vertical velocity of 8.1 m/s, what is the golf ball's resultant velocity? Provide answer in m/s and round to the nearest one decimal place.
a) 9.5 m/s
b) 10.2 m/s
c) 8.4 m/s
d) 7.8 m/s