If ext angle is 105 then extend BC there will be supplementary angles then angle B is75 .ext angle is equal to sum of two interior opposite angles is condition therefore angle A and C is equal and it 52.5 degrees

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Exterior angle of a triangle = Sum of the measures of the two non-adjacent interior angles
Exterior angle of a triangle = 105
105/2 = 52.5
Each of these angles is 52.5 degrees.
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