Connection between 2 Mysql databases

Hi there, I am trying to connect two module databases together which are both built with PHP. Each module is written onto the database and has its own table. The challenge we have, is that we are trying to add and update the data stored from one module which is located on Database A to the second module which is located on Database B and vice versa. So if we do add or update data on module A, we would like it to reflect on the other module B and vice versa. Please note that both databases are located on the same server. Also, please document the changes you make for me. The amount i would like to pay is $15 dollars Thanks in advance