Respuesta :

Answer:

∠ B = 60°

Step-by-step explanation:

The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.

(10x - 45)° is an exterior angle of the triangle , then

10x - 45 = 3x + 4x = 7x ( subtract 7x from both sides )

3x - 45 = 0 ( add 45 to both sides )

3x = 45 ( divide both sides by 3 )

x = 15

Then

∠ B = 4x = 4 × 15 = 60°

clarch19

Answer:

∡B=60°

Step-by-step explanation:

x = 15

so 4x = 60

7x + 180 - (10x-45) = 180

-3x + 225 = 180

-3x = -45

x = 15

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