"How is the banana?"
Translation:केला कैसा है?
The ऐ vowel in कैसा is pronounced like the 'a' in 'bank'.
In contrast to Sanskrit and many other Indian languages where ऐ is pronounced 'ai' and औ as 'au', Hindi (with the exception of a few dialects) does not use diphthong pronunciations for these letters. They are still romanised as 'ai' and 'au' though.
(औ should be pronounced like the vowel in dawn)
ए is pronounced like in 'may' (in the Indian English pronunciation or other accents where it is pronounced with a single vowel). If you know a South Indian language (sorry if I'm wrong about the assumption), it is the same letter (with the same pronunciation) as ஏ/ఏ/ಏ /ഏ.
To distinguish the pronunciations, think of the word 'valet' as in valet parking. The first vowel is close to ऐ and the second to ए.