Using the triangle sum theorem, the value of angle ACB in the triangle is: B. 50°.
What is the Triangle Sum Theorem?
According to the triangle sum theorem, the sum of all the angles in a triangle equals 180 degrees.
90 + 7x - 20 + 4x = 180
70 + 11x = 180
11x = 180 - 70
11x = 110
11x/11 = 110/11
x = 10
m∠ACB = 7x - 20
Plug in the value of x
m∠ACB = 7(10) - 20
m∠ACB = 50° (option B).
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