Which congruence theorem can be used to prove △abr ≅ △acr

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according to the figure, the sides of the two triangles △ABR and △ACR  have specific congruence. 
the congruences are:
AB≅ BC and AR ≅ CR, these mean that the sides are proportional

such triangles are called similar

so  to prove that △ABR ≅ △ACR , we can use SSS theorem
side-side -side Similarity theorem

How many people are we starting with? i will answer it's just i need to divide 8 by the total amount of people to get how many tables