I really don't have much to say here...

${\displaystyle k=ey}$

${\displaystyle k=-e^{ln({\frac {Ji}{1-Ji}})-2ln(S)-xln(A)}}$

${\displaystyle y^{2}={\frac {S^{2}(1-p)+{\frac {kp}{A^{x}}}-TS^{2}}{T}}}$

${\displaystyle y={\sqrt {\frac {S^{2}(1-p)+{\frac {kp}{A^{x}}}-TS^{2}}{T}}}}$