1. 2
2. 1
3. 6
I'll post the rest in the comments
The midpoint of HK would be (4,6). I just used the midpoint formula.
<span>Simplifying
3n + 9 = 7n + -15
9 + 3n = 7n + -15
9 + 3n = -15 + 7n
9 + 3n = -15 + 7n
9 + 3n + -7n = -15 + 7n + -7n
3n + -7n = -4n
9 + -4n = -15 + 7n + -7n
7n + -7n = 0
9 + -4n = -15 + 0
9 + -4n = -15
9 + -9 + -4n = -15 + -9
9 + -9 = 0
0 + -4n = -15 + -9
-4n = -15 + -9
-15 + -9 = -24
-4n = -24
Divide each side by -4
n = 6 </span>