Okay, here we have this:
Considering the provided information, we are going to identify how many orders each of our waiters served, therefore we obtain the following equation (where x represents the number of orders served by Carlos):

Solving for x:

Then, finally we have:
Orders served by Carlos=x=21
Orders served by Deon=2x=2(21)=42
Orders served by Kala=x-7=