If $(3,17)$ and $(9,-4)$ are the coordinates of two opposite vertices of a rectangle, what is the sum of the $y$-coordinates of the other two vertices?
The other two y coordinates are the same as the other ones, respectively.
3,17, so one of the y coordinate is 17
9, -4, so one of the y coordinate is -4
The sum of these two values is 13
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