I got the answer wrong but I need help

"princess tower" in dubai is considered the world's tallest residential building, towering to 1 0 1 101 floors! t ( n ) t(n) models the number of tenants living on floor n n of the tower. what does the statement t ( 2 0 ) = t ( c ) t(20)=t(c) mean?

On a piece of paper graph f(x)=5•(0.4)^x

Ineed to know the answer to this algebra question.