Write a script to calculate the average score and assign a letter grade for each student, also compute the average score for every test (the source data is in the file “grades”). Output all students’ name, scores, and grades in descending order of the average score. Note: please save the output to the file “finalgrades”.
Contents of source data file (grades):
Peter:90:80:70
Alice:79:89:69
David:99:79:89
The final letter grade will be determined based on the following criteria:
A: 90 and above; B: 80 thru 89; C: 70 thru 79; D: 60 thru 69; E; 50 thru 59; F: <50.
Output (finalgrades)



so far i have:

BEGIN{ print "Name   Test1   Test2   Test3   Average   Grade"}
{average=($2+$3+$4)/3;
grade="F"
if (average<50)
grade="E"
if (average<60)
grade="D"
if (average<70)
grade="C"
if (average<80)
grade="B"
if (average<90)
grade="A"
if (average<100)
printf("%-8s%-8d%-8d%-8d%-8d%-8d\n",$1,$2,$3,$4,average,grade)}