The shape is a quadrilateral, because it has four sides.
And sum of angles in a quadrilateral = 360 degrees.
The angle with no number but just a symbol = 90 degrees.
From the fourth angle been M:
Therefore: 90 + 62 + 127 + M = 360
279 + M = 360
M = 360 - 279
M = 81
M = 81°
Option C.
I hope this explains it.
