Your answer is the second option 1,134 mm³.
We can call this shape a prism as it is a triangle at any point, and therefore use the rules for finding the volume of a prism, which is find the area of the cross-section, in this case the triangle, and multiply it by the depth.
The area of the triangle is (14 × 9)/2 = 126/2 = 63 mm².
Then we do 63 × 18, as 18 is the depth, and we get 1,134 mm³.
I hope this helps!