Answer:
x = 23
Step-by-step explanation:
the sum of the 3 angles in a triangle = 180°
the third angle forms a straight angle with 100°, hence
third angle in triangle = 180° - 100° = 80°
Summing the 3 angles gives
2x + 3 + 80 + 51 = 180
2x + 134 = 180 ( subtract 134 from both sides )
2x = 46 ( divide both sides by 2 )
x = 23
