24 mm^2
Reasoning:
The area of the big triangle will be: (6+4+2)(5)(0.5). The answer will be equal to 30 mm^2. The area of the smaller triangle will be: (4)(3)(0.5). The answer will be 6 mm^2. Next, subtract the area of the larger triangle by the smaller triangle (30-6). The final answer will then be 24mm^2.
Sorry if this may have been confusing. I had to do this on my phone.