Justin forms two numbers with the digits $$1$$, $$3$$, $$4$$, $$6$$, $$7$$ and $$8$$. Both numbers have three digits, and each digit is used only once. He adds up these two numbers. What is the greatest sum Justin can get? 
Overseas Competition->Knowledge Point->Counting Modules->Law of Addition and Multiplication->Complex Forming Numbers Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations