Respuesta :

goodingenes
4 sided shapes have internal angles that MUST add up to 360 degrees, so add all four angles to get 360 (opposite angles are equal) so:
8x + 19 + 8x + 19 + 21x - 13 + 21x - 13 = 360
Collect like terms so
58x + 12 = 360
58x = 348
x = 6

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