Hi i have this question

A large food manufacturing company processes and packs leaf tea. One particular section packs tea in boxes. The production process is set so that the combined weight of tea and box is normally distributed with mean 400 gm and standard deviation 14 gm.


Quality control regulations require that no more than 1 box in 40 weighs less than 373 gm.
One day it is discovered that 6% of the boxes produced have weights less than 373 gm. Assuming that the standard deviation has not changed, what has happened to the mean weight of box and tea produced that day?

Could some one explain it to me?

Thanks