What makes you so sure of that.
Cain would negotiate the numbers, and by the way, his 9 9 9 would include that for Social Security, etc. I didnt see that added in to your figures.
Then read it again. I pointed out that the average family of 4 with the median income likely pays nothing but FICA, currently at 5.65%. So Cain's plan is an income tax increase on them right off the bat. Add to that the 9% sales tax on virtually everything they buy and it more than doubles their federal taxes.
FICA is not 5.65%. It is 7.65% x 2 = 15.30% IIRC.