We usually express wages as a rate such as dollars per hour or dollars per year (salary) so the answer depends on how many hours you work.
You could either take your gross pay (total amount of your check before taxes or your hourly rate times the number of hours worked) and add your tips. You then take this amount and divide by the number of hours you worked. This gives you the total amount you made per hour.
The other way would be to take your tip amount ($250) and divide it by the number of hours you worked in the two weeks. Add this amount to the $13 / hour that is your base pay.
I hope this helps!