[tex]\qquad\qquad\huge\underline{{\sf Answer}}[/tex]
The conjugate of given complex number is ~
[tex]\qquad \tt \dashrightarrow \: \overline{z} = - 12i[/tex]
Conjugate of a complex number is the same number with its imaginary part having opposite sign.
Eg. if z = a + i b
Then it's Conjugate = a - i b