Conditional Pop-Up message in excel
 

I am creating a budget template where I want users to add/subtract amounts from their current budget categories but in the end have the current budget amount column b equal the proposed budget amount column f. What coding would I use in VB to create a pop-up message if the total budget in cell b50 does not equal the total budget in cell f50 after their adjustments are made. Furthermore if I have separate budget categories would I use the coding for example for cell b100=f100 on the same worksheet. Thanks in advance.