Answer:
mAngleB = 67°
Explanation:
The angle marked 15x is made by extending one side of the triangle. That is an exterior angle (like, its outside the triangle)
There are two angles inside the triangle that are away from that exterior angle. They are called remote interior angles. They are marked 83° and 6x+7 in this question.
Here's the rule:
If you add up the two remote interior angles it equals the exterior angle.
83° + 6x + 7 = 15x
Subtract 6x.
83 + 7 = 9x
Simplify.
90 = 9x
Divide by 9.
10 = x
Use this to find mAngleB
mAngle B = 6x + 7
= 6(10) + 7
= 60 + 7
= 67
mAngleB = 67°