Normal distribution question

I've got a question here the importants parts of it

regulations say bacteria, per litre of seawater, must be less than 4

rate of occurance of this bacteria at a beach, is 4.6 per litre of sea water

it asks me to say what probabilty distribution to use, i'm sure its the normal distribution

use the distribution to find the prob that this beach will fail the regulations

how am i supposed to do this becasue all the example i have to use the normal distribution involve the mean and sd.

Please could someone explain or solve this for me