I am having issues understanding z score for p value in statistics

I found this similar problem

[Solved] The lengths of pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days. What's the probability of a... | Course Hero

for part B of the problem they ask to find z score for value p, in this example it is 0.03

How do they get to -1.88

In my example I need z score for p value of 0.04