I have a question about how to show the work for this and how to solve it also

Here is the problem:

The verbal part of the GRE has a mean of 500 and a standard deviation of 100. Use the normal distribution to answer the questions:

a. if we wanted to select only students at or above the 90th percentile, what verbal gre score would we use as a cutoff? I got the answer 628.01 but unsure about how to show my work

b.what verbal gre score corresponds to a percentile rank of 15%. 55%?

c what is the precentile rank of a verbal gre score of 628? 350?

d if we randomly selcted 1,500 students who had taken the verbal gre how many would we expect to score lower than 250? higher than 750?