Formula relating time, velocity and acceleration:
Vf = Vi + at (Vf = Final velocity, Vi = initial velocity)
What you're given:
Initial speed, Vi = 5.5 m/s
Acceleration, a = -2.1 m/s^2
Time, t = 0.3 s
Required:
Vf = ?
Plugging in the given information:
Vf = (5.5) + (-2.1)(0.3)
Vf = 4.87 m/s
The bicyclist's speed is 4.87 m/s after 0.3 s.
