If we apply the distributive law to right side of the third choice we get:-
-12x - 9 = -9 - 12x
right side = left side so infinite solutions
The kite is symmetric about line segment BD.
Therefore
AB = BC
3x + 1 = 22
3x = 22 - 1 = 21
x = 21/3 = 7
Similarly,
AD = CD by symmetry
Therefore
4x = CD
4*7 = CD
28 = CD, the required line segment
Answer: 28
To subtract vectors, you simply have to subtract correspondent coordinates.
So, if you have

the subtraction is simply

So, in your case, we have
