A motorbike accelerates uniformly at 0.6m.s for 10s. If it covers a distance of 500m. During this time, what was its initial velocity?

The acceleration should have units of m/s^2 so I will assume it is

0.6 m/s^2

The average velocity during the period is 500/10 = 50 m/s = (V2 + V1)/2, so

V2 + V1 = 100

You also know that
V2 - V1 = a * 10s = 6 m/s

Therefore
2 V2 = 106
V2 = 53
V1 = 47 is the initial velocity