Answer:
x = 143
Explanation:
You want the fourth angle when three of the angles around a point are given.
Angle total
The total of angles around a point is 360°. That means ...
x° +51° +39° +127° = 360°
x = 360 -217 . . . . . . . . . . . subtract 217 and simplify
x = 143
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Additional comment
This means the figure is not drawn to scale, and the diagonal is not a straight line.