$($a$)$ The stepwise equilibrium constants $($K$)$ for the reaction of Cd$2+$ ions with ammonia at $25\backslash$deg C are as follows:$[$Cd$($H$2$O$)6]2++$ NH$3[$Cd$($NH$3)($H$2$O$)5]2++$ H$2$O log K$1=2\mathrm{.}75[$Cd$($NH$3)($H$2$O$)5]2++$ NH$3[$Cd$($NH$3)2($H$2$O$)4]2++$ H$2$O log K$1=2\mathrm{.}20$Calculate the value of log $2$ for the formation of $[$Cd$($NH$3)2($H$2$O$)4]2+$