Is this correct when calculating acceleration

If we have an Initial velocity of 0 km/hr, and a final velocity of 24 km/hr, and a time of 3 seconds, would it be OK to convert the units in the velocities?

For example, 0 km/hr = 0 m/s
24 km/hr = 24000m/hr = 24000 m/3600 s = 20/3 m/s.

Is the acceleration 20/3 m/s /3 s = 20/9 m/s^2 ?
Is the conversion a valid way to do this problem?

Any help would be appreciated.

You are absolutely correct.
It is a necessary step in all problems to convert the units to appropriate ones ( normally SI units).
And your answer is also correct.