Give me sample rate/ratio questions

The lengths of nails produced in a factory are normally distributed with a mean of 4.91 centimeters and a standard deviation of 0.05 centimeters. find the two lengths that separate the top 4% and the bottom 4%. these lengths could serve as limits used to identify which nails should be rejected. round your answer to the nearest hundredth, if necessary.

What is the number 321,000,000 in scientific notation? also what is the number? ?

Ijust need to see how to do this. so you don’t have to answer all of them just a step by step explanation of one.