Well, I've never coded in VB in my entire life, but here goes.
Make a variable for each test score, each test average and the percentages for each section as given by the user.
Dim testpercent, labpercent, quizpercent, finalpercent As Decimal
Dim test1, test2, test3, testaverage, lab1, lab2, lab3, lab4, lab5, labaverage, quiz1, quiz2, quiz3, quiz4, quiz4, finalexam, classaverage As Integer
To make sure user input works correctly, first ask the user what the section percentages are supposed to be. I'm not sure if you're supposed to have them input the percent or the decimal, so I'm gonna go with percent.
Console.Write("What percent of your grade is your test average? (0 to 100 ")
testpercent = Decimal.Parse(Console.ReadLine())/100
Console.Write("What percent of your grade is your lab average? (0 to 100) ")
labpercent = Decimal.Parse(Console.ReadLine())/100
Console.Write("What percent of your grade is your quiz average? (0 to 100) ")
quizpercent = Decimal.Parse(Console.ReadLine())/100
Console.Write("What percent of your grade is your final exam? (0 to 100) ")
finalpercent = Decimal.Parse(Console.ReadLine())/100
(the /100 turns it into decimal form, like 40 to 0.4)
Now set the all the test/quiz/lab variables to whatever they're supposed to be equal to and set the testaverage to their average.
Console.Write("What is your first test grade?")
test1 = CInt(Console.ReadLine())
Console.Write("What is your second test grade?")
test2 = CInt(Console.ReadLine())
Console.Write("What is your third test grade?")
test3 = CInt(Console.ReadLine())
testaverage = ((test1,test2,test3)/3 ) * testpercent
This SHOULD set your testaverage to the portion of your final score it's equal to. If your test average is 90 and the user entered 35 for testpercent, testaverage will become 90*0.35 or 31.5
Repeat this for the quizzes, labs, their averages, and finally the exam. For the final exam, you obviously don't have to average anything: just multiply finalexam by finalpercent.
Finally, to get user's score in the class
once all of that has been done, you can just sum the portions:
classaverage = testaverage + quizaverage + labaverage + finalexam
Lastly, for the A-B-C etc thing, you can just use an if statement:
If (classaverage>=90) Then
Console.WriteLine("Your score in the class is: {0}. You made an A in the class!",classaverage)
ElseIf (classaverage>=80) And (classaverage<90) Then
Console.WriteLine("Your score in the class is: {0}. You made a B in the class!",classaverage)
ElseIf (classaverage>=70) And (classaverage<80) Then
Console.WriteLine("Your score in the class is: {0}. You made a C in the class!",classaverage)
ElseIf (classaverage>=60) And (classaverage<70) Then
Console.WriteLine("Your score in the class is: {0}. You made a D in the class!",classaverage)
Else
Console.WriteLine("Your score in the class is: {0}. You made an F in the class!",classaverage)
End If
Again, I've never used vb.net in my life, so this is all guesswork from googling. It may not work, and even if it does, it's guaranteed poor code. Still, if it does work, that's awesome, and if you get errors, let me know. Good luck.