Counting Grades to print - python-3.x

Question

Hopefully this will be very simple all I need help with is getting a count of the letter grades and then printing them along with the list.
Here is my code:
def getScores():
f_obj = open("scores.txt", "r")
data = f_obj.readlines() #read file into a list of record strings
f_obj.close()
return data
def displayData(data):
print("Name Avg Grade")#print headings
for record in data:
name, ex1, ex2, ex3 = record.split()
exam1 = float(ex1)
exam2 = float(ex2)
exam3 = float(ex3)
avg = round(exam1 + exam2 + exam3) / 3
if avg >= 100:
letterGrade = "A"
elif avg >= 89:
letterGrade = "B"
elif avg >= 79:
letterGrade = "C"
elif avg >= 69:
letterGrade = "D"
elif avg >= 59:
letterGrade = "F"
Just above here is where im stuck I cannot figure out how to do a count with the certain letter grades.
print("%-10s %5s %5s" % (name, round(avg, 1), letterGrade))
print()
print(
def addStudent():
name = input("Enter student name: ")
ex1 = int("Enter Exam 1 grade: ")
ex2 = int("Enter Exam 2 grade: ")
ex3 = int("Enter Exam 3 grade: ")
return name + "\t" + ex1 + "\t" + ex2 + "\t" + ex3
def storeData(data):
f_obj = open("scores.txt", "w")
f_obj.writelines(data)
f_obj.close()
def main():
scoreData = getScores() # read data file into a list
while True:
print("""
Program Options
1.) Display Students.
2.) Add a new student:
3.) Exit Program """)
option = input("Enter option 1, 2, or 3: ")
if option == "1":
displayData(scoreData)
elif option == "2":
scoreData.append(addItem()) # add record string to our list
elif option == "3":
storeData(scoreData)
print("Good bye.")
break
else:
print("Not a valid entry. Please enter 1, 2, or 3.")
main() # start the program

Answer 1

Hint: you already know how to determine if a grade is an A, B, C, etc. So all you need to do is increment a counter at the same time.
For example, you'd add in something like this to count the number of A grades:
if avg >= 100:
letterGrade = "A"
numAs += 1
Then do the same thing for each other grade type. Since this appears to be homework, I'll let you figure out how to do all this. Most importantly, even though Python isn't strict about this, think about the correct place to declare the counter variables.
Once you've got that working, here's an "extra credit" assignment: see if you can do all that using just a single array.