Answer:
The first one
Step-by-step explanation:
I believe it is the first option, as you can see that, on the right hand side, 4a was multiplied to the first term to make a common denominator. I'm sorry if it is wrong, and I hope this helped.
The answer is 3 for sure.
Answer:

Step-by-step explanation:
The area of the big triangle is 1/2 b h = 1/2*6*(12^2 = 6^2 + x^2)
that ends up being 
the small triangle are needs to be subtracted....
that is the length of the unknown side...
1/2 B * h of that triangle get you to 
just subtract the two areas