Sum Values in Second Column where First Column Meets condition in Google Sheets

I'm using google sheets to collaborate with others on an event. There are four columns in total:

Name,Table No, N.Guests, Total on Table

John Smith, 1, 2, Y1

Andrew Smith,1,3, Y2

Michael Smith,2,4, Y3

I'm looking for a way to sum over all the number of guests who are on the same table. I don't see how a simple if statement would do that. Is a custom function required and how would I do this?

If it were in python I would write a loop and have an if statement to check the table number and some over only those that meet the condition.

Is there a way to do this with google sheets?