Simple....
to solve for this-->>
Using the formula for area of a right triangle-->> [tex] \frac{1}{2} bh[/tex]
For both triangles it'd be the same formula-->>[tex] \frac{1}{2} 4*3[/tex] (The base is split in half as it is two triangles)
=6
Now since there's two triangles-->>6+6=12[tex] yd^{2} [/tex]
Thus, your answer.