Well i personally would create variables for user input.
But my code would look like this:

dim sngInput1 as single
dim sngInput2 as single
dim sngInput3 as single
dim sngInput5 as single
dim sngInput6 as single
dim sngInput8 as single
dim sngInput9 as single
dim sngoutput1 as single
dim sngoutput2 as single
dim sngoutput3 as single

snginput1=val(textbox1.text)
sngInput2=val(textbox2.text)
snginput3=val(textbox3.text)
snginput5=val(textbox5.text)
snginput6=val(textbox6.text)
snginput1=val(textbox8.text)
snginput1=val(textbox9.text)


sngOutput1=sngInput1-sngInput2+sngInput3
Label1.text=sngOutput1


sngOutput2=snginput4 - snginput5 + snginput6
Label2.text=sngoutput2

sngoutput3=snginput7 - snginput8 +snginput9
Lbel3.text=sngoutput3

I would use a single data type b/c I dont know how big or small the numbers the users are inputing are.
I would also use labels for the output numbers b/c i dont see any reason why they need to be textboxes since the user is not inputing anything into them.
If you want the code to execute when the textchanges just copy and paste the code for the given equation in each of the 2 or 3 textboxes that are in the formulas...
hope this helped

DDT