The sum of angles of a triangle is 180°.
84 +(x +59) +(x +51) = 180
2x +194 = 180 . . . . . . . . . . . . . collect terms
2x = -14 . . . . . . . . . . . . . . . . . . subtract 194
x = -7 . . . . . . . . . . . . . . . . . . . . divide by 2
The value of x is -7.
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The three angles are 84°, 52°, 44°.