That point of concurrency is known as the incenter of a triangle.
for question #1 the answer is: x=2, x=-1
question 9: answer is B
question 10: answer B
The answer is D. "x=-15 or 15."
You can solve this by adding seven on both sides.
|x|-7=8
+7 +7
------------
|x|=15
Therefore, x is either equal to 15 or -15.
Number 4 is a, and 6 is d, but I'm not sure about 5