a,538 = 5 . 100 + 3 . 10 + 8 = 5 . 10^2 + 3 . 10^1 + 8 . 10^0
b,8609 = 8.1000 + 6.100 + 9.1
= 8.10^3+6.10^2+9.10^0.
c) abc = a.100 + b.100 + c.1
= a.10^2+b.10^1+c.10^0
d,abcd = a . 1000 + b . 100 + c . 10 + d
= a . 10^3 + b . 10^2 + c . 10^1 + d . 10^0