Simple operation in vbscript (Zebra Designer Pro)


How do I perform a basic substraction operation in Vbscript?
I have to enter a gross weight, subtract 25 and put it as net weight. It's always 25. What would be the correct sintax?
I will explain what I want:

I'm making a label with a lot of variables. You enter a series of data and some codebars are being completed as you go. It's as simple as when you get the gross weight, you substract the tare (also asked as a variable) from it and get net weight. In this way:

When I get to print the label, in this part:
I get this error message, at first:

And this at second try:

Feel free to ask for anything you need about this.

primero.jpg (58.89 KB)
cuarto.jpg (10.93 KB)
tercero.jpg (16.72 KB)
segundo.jpg (224.58 KB)