Can I add custom fields using Page composer and do some calculation on basis of those values

Summary:

There is a requirement to store Units on the Project and use that information on the Contract line level and Event level.

Let's say on a Project there are 100 units (stored in a custom field) initially. I created a contract using that Project and on the contract line, I used 40 units (populated on a custom field). So next time I try to use that Project on a different contract line, the requirement is to select units from the available 60 only.

Can I achieve this requirement using page composer or any standard field if I can use it?