Dont read this if you dont want to know the answer just yet (THAT WAS YOUR SPOLIER ALERT ;)
6 + 3 = 39 ..... (6-3 gives the first number = 3, then ad the numbers together 6 + 3 = 9, then put them side by side giving 39)
9 + 4 = 513 .... (9-4 gives 5, 9+4 gives 13, making 513)
Therefore
18+16 = 234 .... (18-16 gives 2, 18+16 gives 34)
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