15. Solve for x.
71°
(10x + 6)
(13x - 2)
(8x - 1)

x = 8

Step-by-step explanation:

Measure of unknown angle 'y' = 180° - 71° (linear pair of angles)

                                                   = 109°

Formula for the interior angle of a polygon = (n - 2) × 180°

Here n = number of sides of the polygon

Therefore, sum of the interior angles of the given polygon = (4 - 2) × 180°

                                                                                                  = 360°

(10x + 6) + (13x - 2) + (8x - 1) + y = 360°

(10x + 13x + 8x) + (6 - 2 - 1) + 109 = 360

31x + 3 + 109 = 360

31x + 112 = 360

31x = 360 - 112

31x = 248

x = 8

if x = 1, then the answer is 3.5