5 1/2 + p = 6
subtract 5 /12 from each side
5 1/2 - 5 1/2+ p = 6 - 5 1/2
p = 6 - 5 1/2
borrow from the 6
p = 5 2/2 - 5 1/2
p = 1/2
Use the midpoint formula.
(x1+x2)/2 , (y1+y2)/2
Then you should be able to find the reflection line based on where the middle of the two points are.