Answer:
<h2>c. 16.5</h2>
Step-by-step explanation:
It's the right triangle.
The formula of an area of a right triangle:

Look at the picture.
We have

Substitute:

Answer:
C is the most reasonable answer because to add the system of equations together, you must make sure that one of the terms (whether it be the x or y value) can cancel out.
Step-by-step explanation:
Multiply the equation:

The solution set is the same, because multiplying both sides of an equation by a non-zero number doesn't change the solution set. In fact, if you rewrite the equation as

Multiplying this by 3 (or whatever number, for all it matters) gives

Now, a product is zero if and only if at least one of the factor is zero. So, either
or 
Since the first is clearly impossible, the second one must be true, which is the original equation.