Step-by-step explanation:
2 things to remember :
1. the sum of all angles in a triangle is always 180°.
2. the sum of all angles around a single point on one side of a line is also 180° (because the line can be seen as the diameter of a circle, the point as its center, and so every side of the line is a half-circle = 180°).
so, the third, unnamed angle in the triangle is the supplementary angle to 142° (that means they complete each other to full 180°).
it is therefore
180 - 142 = 38°
and then, inside the triangle
180 = 66 + x + 38 = 104 + x
x = 76°
