import math
def z_test_statistic(sample_mean, pop_mean, pop_std, n):
se = pop_std / math.sqrt(n)
return (sample_mean - pop_mean) / se
# Known population std dev (sigma) from historical data = 15
z = z_test_statistic(sample_mean=104, pop_mean=100, pop_std=15, n=40)
print("z =", round(z, 3))