Answers:
question one: 6
question two: 1/3
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Step-by-step explanation:
The side 12 from triangle A corresponds to the side 4 from triangle B.
The scale factor is A/B = 4/12 = 1/3 which tells us that sides in triangle B are 1/3 as long compared to sides in triangle A. This takes care of the second question.
We'll use this scale factor to determine the missing side of triangle B.
The side 18 in triangle A corresponds to this missing side in triangle B.
Take 1/3 of 18 to get (1/3)*18 = 6 which is that missing side.
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Another way to look at it: Take any side of triangle B, triple it, and you'll get a corresponding side of triangle A.
Example: The jump from 5 to 15 is "times 3".