Respuesta :

Answer:

40

Step-by-step explanation:

Exterior angle Theorem: the sum of the 2 farthest angles from the "outside"/exterior angle is equal TO the exterior angle.

So,

80 = (19x + 2) + (-2+21x)

80 = 40x

x = 2

m<ABC = 19(2) + 2 = 40

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