You use x1-x2 over y1-y2
So -4-3 = 1 and 6- -7 is 1 so it’s 1/1. That’s the slope.
It can work well here to simplify inside parentheses first.

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The correct selection is not show with your problem statement.
I would set this up as a a proportion:

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17x = 1360
x = 20 cm