The midpoint formula tells you that the a segment with endpoints (a, b) and (c, d) will have a midpoint at ((a + c)/2,(b + d)/2)

So we know that (x + 9)/2 = 6 and (5 + y)/2 = 3. We can solve those!

(x + 9)/2 = 6
x + 9 = 12
x = 3

(5 + y)/2 = 3
5 + y = 6
y = 1

Therefore, x + y = 4.

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