help please

#1
A teacher gives a 20-point test to 12 students. The scores are shown below.
18 17 12 8 8 17 3 7 12 10 20 12
Find the following:
  • Mean
  • Mode(s)
  • Range
  • Quartiles
  • Standard Deviation
  • The teacher forgot to add the grade of the 13th student, when he did do, the mean of the class was 12.5. What was the student’s grade?