Field calculate the revenue from other record.

Hi All,

I have One Custom Entity called Business Investor and in that I have one custom field called Revenue currency type.

My requirement is whatever I give in Revenue field for particular customer. It should Update in Contact Form Annual Revenue which is whole number . for example: I'm creating Business Investor Record 

For Customer Alok I'm giving Revenue 15000 and again creating one record for that also Customer Alok and Revenue 13000 So on Contact form Alok : Annual Revenue should reflect 28000(15000) because Customer is same for both Business Investor Record .

Please let me no How I can do by javascript.