Melissa, juan, and rafael served a total of 74 orders monday at the school cafeteria. rafael served 2 times as many orders as juan. melissa served 6 more orders than juan. how many orders did they each serve?

Let's named variables as M,J and R

The equation is M+J+R=74

We will represent M with J => M=J+6 and R=2J

when we replace in the equation we get

J+6+J+2J=74 => 4J=74-6 => 4J=68 => J=68/4 = 17

J=17  => M=6+17 => M=23  and R=2* 17 => R=34

Final answer is 
Juan served 17 orders
Melissa served 23 orders and 
Rafael served 34 orders

Good luck