Angles
We have completed the figure to show a new variable:
The angle of 158° and angle k form a line, so these angles are complementary, i.e., they add up to 180°:
158° + k = 180°
Solving for k:
k = 22°
Now we know the value of k, we observe that there are four d's, 38°, and k that add up to 180°:
4d + 38° + 22° = 180°
Simplifying:
4d + 60° = 180°
Subtracting 60°
4d = 120°
Thus:
d = 120/4
d = 30°