the extended line(the base and the line that extends past the triangle) is 180°. With an extended line that is 180°, the inside angle must be 180° - the outside angle, and the outside angle must be 180° - the inside angle. if the angle on the outside is 127°, then the inside angle(x) should be 180° - 127° or 53°.
to verify: all the inside angles must equal to 180°
the angle on the top is 90°( when there is that square thing on an angle it means it is 90°) and the angle on the right is 53°, so the remaining angle is 180 - (90° + 53°) or 37°.
