All the angles inside a triangle add up to 180°.
(2x + 15) + (5x + 5) + x = 180
8x + 20 = 180
8x = 180 - 20
8x = 160
x = 160/8
x = 20
the question is asking what angle B is,
B = 2(20) + 15
B = 40 + 15
B = 55°
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given
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Reason: Reflexive property
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ASA