Suppose that people's heights (in centimeters) are normally distributed,
with a mean of 170 and a standard deviation of 5. We find the heights
of 90 people. (Round answer to the nearest whole number.)

It's not to difficult if you know the basics for example how many would you expect to exceed 170 cm tall would be (b)
P(X > 170)
= P(Z > (170 - 175)/6)
= P(Z > -5/6)
= 0.79767
0.79767 x 60 = 47 people (round down)