∠A=5x−15

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start color #11accd, angle, A, end color #11accd, equals, start color #11accd, 5, x, minus, 15, degrees, end color #11accd \qquad \green{\angle B} = \green{2x +21^\circ}∠B=2x+21

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Here we have two congruent angles ∠A and ∠B. Remember that angles are congruent if they have the same measure, so:

Substituting x in one angle:

i found two solutions,   n = 2 • ± √3 = ± 3.4641

step-by-step explanation:

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)