Answer: D. 
Step-by-step explanation:
Given : The charge of painting = $2 per square yard
Let x be the total cost of painting the triangular wall .
The base of the triangular wall = 4 yards
The height of the triangular wall = 6 yards
We know that the area of the triangle = 
Thus, the area of the triangular wall = 
Now, the total cost of painting the triangular wall =
Hence, the total cost of painting the triangular wall 