1. 12/04/1996 is one-two/zero-four/one-nine-nine-six
This word representation contains 6 / 8 / 14 letters hence code is 6814.
2. 11/05/2003 is one-one/zero-five/two-zero-zero-three
This word representation contains 6 / 8 / 16 letters hence code is 6816.
3. 21/09/2009 is two-one/zero-nine/two-zero-zero-nine
This word representation contains 6 / 8 / 15 letters hence code is 6815.
Similarly
18/09/2013 is one-eight/zero-nine/two-zero-one-three
So this word representation contains 8 / 8 / 15 letter hence code is 8815.
option 5
Do not worry about your difficulties in mathematics, I assure you that mine are greater.
Albert Einstein
Pure mathematics is the world's best game. It is more absorbing than chess, more of a gamble than poker, and lasts longer than Monopoly. It's free. It can be played anywhere - Archimedes did it in a bathtub.