Answer :
6 - a = 1/3(9a - 18)
6 - a = 3a - 6
-a - 3a = -6 - 6
-4a = -12
a = -12/-4
a = 3..........one solution
6 - a = 3a - 6
-a - 3a = -6 - 6
-4a = -12
a = -12/-4
a = 3..........one solution