mean score/standard deviation/distribution table

HI!
Can someone please explain to me how do I calculate questions like this one?

The results of an accountancy exam are normally distributed with a mean score of 58 and a standard deviation of 10.
What is the percentage probability that a student will score more than 80 (to 2 decimal places)?

OR
A probability of 2.28% will have been determined from the normal distribution table. The normal distribution value which will give this probability is 0.4772 (0.5 – 0.0228)
This value equates to a Z-score of 2 from the normal distribution table.
Z-score = (x – µ)/?
2 = (90 – 70)/?
? = 20/2 = 10

I am just looking for some formula someone could explain it to me.
I keep having these kind of questions.
I have already ask John one of these questions but I havent really understand anything from his answer.

Just now I had again similar question in Mock test
The number of daily complaints to a local government office has a standard deviation of 7 and the coefficient of variation is 20%.
What is the mean number of daily complaints?

Is there any videos, resources etc which could explain it to me step by step.
Thank you