What Is The Other Missing Number?

Logic Level 3

$\LARGE{\begin{eqnarray} \boxed{\phantom0} \; + \; \boxed{\phantom0} \; - \; \boxed{\phantom0} \; &=& \; \boxed{\phantom0} \\ \boxed{\phantom0} \; \times \; \boxed{\phantom0}\; \div \; \boxed{\phantom0} \; &=& \; \boxed{\phantom0} \\ \end{eqnarray}}$

Put one of the integers $$1, 2, \ldots , 9$$ into each of the boxes, such that eight of these numbers are used once (and one number is not used at all) and both equations are true.

What is the sum of all possible values of the missing number?

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