[(49.4 m/s)-(3.1 m/s)]/10 s=average acceleration
Our first priority is to verify that units match.
The left side is m/s every second. That is the definition of acceleration.
(46.3 m/s)/10 s=average acceleration
4.63 m/s2=average acceleration
Is this the answer you had?
If the units match, you should have the correct answer.