SUMX - How do sum information from one table into another

I would like sum in a lookupvalue. Is that possible or is there another command(s) that I need to look at to achieve my desired outcome?

I have a budget table with a field and would like to scan a transaction table with the same field name. How do I sum all the transactions and put the total into the budget table?

I am wanting to sum the transactions to the corresponding field(s) in the Budget Table.