If 70% of a no. Is subtracted from itself it reduces to 81.what is two fifth of that no.? 108/54/210/none

Suppose n is used to represent the number.
  n - .7n = 81
  n = 81/.3 = 270
  2/5*270 = 108

X-0.7x=81
1-0.7=(81/x)
x(1-0.7)=81
x=81/(1-0.7)
(2/5)(81/(1-0.7))=108