Help figuring out probability question(s)

Hi everyone this is a two part question and I can't seem to get the right answers using the z score formula's associated with this problem.
The question is:

Bupropion and Nicotine are the most common methods utilised in assisting smokers to quit their addiction. Unfortunately, these methods aren't effective for everyone, with approximately 45% of people relapsing. Assume time taken to relapse is normally distributed with a mean of 8.5 days and a standard deviation of 1.9 days, answer the following questions:

a) What is the probability that a randomly selected smoker will relapse in less than 10 days?

b) What is the probability that a randomly selected smoker will have a relapse between 5 and 10 days?

the associated formula is z = x-u(mean)
------------
(standard deviation)

There is more to it with z tables and finding probability between two values but hopefully people can help me find and understand the correct answer.

Thanks