Question 1021141
Hi there,
Looking at the face of the trench
it can be divided into a rectangle in 
the middle of two triangles.
Area of rectangle = 3m x 10m = 30 m^2
Area of two triangles together 
1/2 (3 x 10) = 15 m^2
Total face area = 30 + 15 = 45 m^2
Face area x Length
45m^2 x 150m
= 6750 m^3
This is the amount of earth removed.
Hope this helps :-)