In a code language, 'chores are hobbies' is written as 'tpl esr nil', 'hobbies keep me busy' is written as 'cha esr lon ane', 'busy with chores' is written as 'sia ane nil'. What is the code for the word 'with' in this language?

Let's isolate the codes for each word step-by-step:
Compare sentence 1 and sentence 2:

'chores are hobbies' → 'tpl esr nil'

'hobbies keep me busy' → 'cha esr lon ane'

Common word is 'hobbies', so code for 'hobbies' = 'esr'.

Compare sentence 1 and sentence 3:

'chores are hobbies' → 'tpl esr nil'

'busy with chores' → 'sia ane nil'

Common word is 'chores', so code for 'chores' = 'nil'.

Compare sentence 2 and sentence 3:

'hobbies keep me busy' → 'cha esr lon ane'

'busy with chores' → 'sia ane nil'

Common word is 'busy', so code for 'busy' = 'ane'.

Now examine sentence 3:

'busy with chores' → 'sia ane nil'

We already know: 'busy' = 'ane' and 'chores' = 'nil'.

The remaining word is 'with', and its corresponding remaining code is 'sia'.

Hence, the code for 'with' is sia.