Since it's an estimate, it wouldn't be the exact answer.
Therefore, I'd say it's about 48, considering 6 * 8 = 48. However, if you wanted to round the 8 up since the decimal is quite high, then it would be 6 * 9. Which equals 54.
If it were me, I'd answer 54 because of the decimal being as high as it is, but it's up to you.
Hope this helped! :)