we have,
|f-6| = |f+8|
we will get two equations,
f-6 = f+8, which cannot be true
Here, f cannot be a real no.
f-6 = -(f+8) --- (2)
=> f-6=-f-8
=> 2f = -2
=> f = -1
Since the equation 1 cannot be true it is rejected, we take the value of f from the equation 2
Hence the value of f is -1