Which best explains why these two figures are similar or not similar?

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Answer:
These two figures are similar because 5/3 equals 15/9.
Step-by-step explanation:
These figures are similar to each other, which means the side-lengths are proportional. Therefore:
[tex]\frac{5}{9} = \frac{15}{9}[/tex]
Side-lengths 15 and 9 are proportional to 5 and 3 because the two fractions are equivalent; the larger rectangle is just 3 times larger.