Answer: 105
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Step-by-step explanation:
We can apply the remote interior angle theorem. Some math books or teachers may refer to this as the "exterior angle theorem". They're the same idea just with different names.
According to that theorem, the interior angles x and 53 add up to the exterior angle 158
x+53 = 158
x = 158-53
x = 105
This theorem only works if neither interior angle is adjacent to the exterior angle. Hence the "remote" part.
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If you wanted a slightly longer approach, then let y be the missing angle that isn't marked in the diagram. Angle y is adjacent to the 158 degree angle.
We can find y by noting how 158 and y are supplementary
158+y = 180
y = 180-158
y = 22
Then we use the fact that adding three angles of any triangle always gets us 180 degrees
x+y+53 = 180
x+22+53 = 180
x+75 = 180
x = 180-75
x = 105
Effectively, this example helps reinforce why the remote interior angle theorem is true.