Answer:
the SSS similarity theorem
Step-by-step explanation:
The triangles are not indicated as being right triangles (even though we know they are), so we cannot use the HL theorem.
The ratios of corresponding sides are the same, so the applicable theorem is ...
the SSS similarity theorem
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3/(3+6) = 4/(4+8) = 5/15 = 1/3 . . . the ratio of shorter sides to corresponding longer sides.
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<em>Additional comment</em>
You recognize the smaller triangle as a 3-4-5 right triangle, and notice that the larger triangle is 3 times that size. If angle C were marked as the right angle it is, then the HL similarity theorem could also be used.
