Finding the z score for a hypothesis test

Help! I'm working on a project that is due at the end of the week and I can't figure out the z score for this hypothesis test.

According to the US Census, 38% of college students are over the age of 25. Out of the 60 students randomly surveyed, 20 said that they were over the age of 25, so 33%. at 5%, is the percentage of students at this college less then the nationwide average?

H0: p=.38
H1: p<.38
a = .05
n = 60
x = 20/60 = .3333

I'm really lost and don't know where to go from here. If you can, please help. Thank you :)