ทำไม

[tam yaa raa aa paeng khà nàat níi]

Why is the food so expensive? (situation: restaurant inquiry)

Used when questioning prices.

[tam yaa khun mâi toh hǎa chǎn]

Why didn't you call me? (situation: personal question)

Asking for explanation.

[tam yaa wan níi khun mâai tham ngaan]

Why aren't you working today? (situation: office conversation)

Common usage and polite tone.