Auto increment numbers on an Excel user form

I have an inventory form and I need to auto increment the numbers as new parts are added. I need the system to add it based upon the last number entered plus 1 when the add button is selected and the part description has been entered, it needs to be added with the number to the type that it is: example: LA-0001... if entering a new ladder... it would be LA-0002, DR-0001.... if entering a new drill it would be DR-0002.

if this doesn't make since, sorry!

I know this is doable.. but not sure where to start with the coding.

I have the form created but only coded the buttons to open the form. I have attached the file in case it needs to be viewed.

cinstanl