The answer to this question is -21
Answer:
w=15
Step-by-step explanation:
Hey there mate!
Please check the attached answer of picture for explanation.

A would be (-3, 6).
B would be (-6, 3).
Anytime something is asking you to reflect off of the Y-axis, you put the original but flipped. Also, your answer will always be straight across vertically.
((-9+14)/2, (-20+12)/2)
(5/2,-8/2)
(5/2,-4)