To celebrate $2019$, Faraz gets four sandwiches shaped in the digits $2$, $0$, $1$, and $9$ at lunch. However, the four digits get reordered (but not flipped or rotated) on his plate, and he notices that they form a $4$-digit multiple of $7$. What is the greatest possible number that could have been formed?

Let's think step by step and output the final answer within \boxed{}.
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