$($b$)$ A $6-$bus system with two Power Voltage busses namely bus number $3$ and bus number $6.$ The slack bus is bus number $5.$ The line connection of the system is as follows: $1-2,1-3,1-6$; $2-3,25$;$3-5,3-6$;$4-5$;$5-6.$ Write down the bus voltage equations of the $5$ th iteration only for bus $1,2,$ and $3,$ using Gauss$-$Siedel Iterative method.

$[9$ marks$]$