Answer: KD is 109 units long
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Step-by-step explanation:
Draw out a number line. Plot point D at -84 and K at 25. Plot a third point, say point A, at 0.
From D to A is 84 units
From A to K is 25 units
Those two distances add to 84+25 = 109 units total, which is the distance from K to D on a number line. This is the same as the length of segment KD.
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You could also show your steps like this
|D - K| = |-84 - 25| = |-109| = 109
The absolute value is to ensure the result is never negative.
The D and K can swap like so
|K - D| = |25 - (-84)| = |25+84| = |109| = 109
Either way we get the same distance.