Multiplying And Calculating Net Using VBA With Output Using MsgBox

I have to complete the following project in visual basic for Excel

direction quantity price
b 400 10
b 100 20
s 900 15

So the above is a small sample space of what i have(over 3000 rows in total) they are stocks. if there is a "b" in the direction that denotes a negative (short) and if there is an "s" (long) that denotes positive.

Two parts:
1) Write a traditional macro (with button) that when pressed, will give the total Net value in a message box.
2) Secondly, write the code in 'class module' that give me the over all net value in a message box.

I understand what I need to do but just don't know how to write the code for this in visual basic.

So for the above example the net would be -400(10) -100(20) + 900(15) = +$7500

But how can I write a program to do this and display the final answer in a message box?

Exercise.xlsm