Assume that the mean salary for a profession is $35,104 with a standard deviation of $3200. What percent of the profession earns less than $38,700?

I don't understand how to do this.
Please help!!

I went to

http://davidmlane.com/hyperstat/z_table.html
and entered the values to get

.8694

This is a routine question. I don't know if you use tables in the back of your book or use a webpage like I linked to.
If you are studying this topic, your statement of
"I don't understand how to do this", puzzles me.