For the bottom, to find the top side of the triangle, 10-4, as seen from the top and bottom sides of the rectangle. So 6.
To find the left side of triangle, subtract 12 from 8. 12 from the left and 8 from the rectangle. This gives you 4.
Now that we have 6 and 4, we can find the area:
A= ab/2
A= (6*4)/2
A=24/2
A=12 mm^2
