When a particle travels in a circular orbit of radius 14.9 m and its speed is changing at a rate of 10.7 m/s² when its speed is 34.5 m/s, what is the magnitude of its acceleration?
a) 4.5 m/s²
b) 6.5 m/s²
c) 8.5 m/s²
d) 10.5 m/s²