add a total row to side-by-side or dropdown options to a constant sum.

Hi,
I would like to create a table were respondents are faced with three products and they have to assign either 30 tokens or 60 tokens to each one of the three products. the total number of tokens they can use is 120, i.e. their budget.
I've tried using a side-by-side question but was not able to add a total row that shows respondents if the tokens allocated to each product is within their budget.
I then tried to use a constant sum question however I was not able to limit entires to either 30 or 60 . it seems like you can enforce a range but not provide a limited number of options in a dropdown list.
Does someone know how to do this?
Thank you very much!