Future Iron Man Contest -part 1(Q-2)

Iron Man and Bruce Banner are trapped by the evil THANOS .In their cells Iron Man can see 12 trees and Bruce banner can see 8 trees.They are told that together they can see all the trees in prison and the dont see a common Tree.No one knows the no of trees other person can see. Every day Thanos visits iron man and asks "Are their 18 trees or 20 trees in total ?'If he passes the question to bruce,then bruce is asked the same question.If he passes the question too,Process is repeated the next day.If anyone answers and he answers wrongly,Both of them are killed by thanos using his infinity gauntlet .If one answers correctly,Both are set free!!!! Q-On which day they both escape? Note-if u think they cant escape ,Enter your answer as 998.324 If the no of days is $x\quad then\quad the\quad answer\quad is\quad (logx)^{ 2 }.If\quad (logx)^{ 2 }\quad is\quad an\quad integer\quad then\quad answer\quad is\quad x+0.324$ Here log base 10 is to be taken