Translation:Six ladies drive the new cars.
bantiarna is a compound word - tiarna is the Irish for "lord", and ban indicates that it's a woman-lord - i.e. a lady. The nt isn't a cluster, and the broad/slender rule doesn't apply across the join in a compound word.
The exception is that compound words get their gender from the second part, but bantiarna is a feminine noun, even though tiarna is masculine.
A basic spelling rule is 'leathan le leathan, caol le caol' ('broad with broad, slender with slender'). What this means is that consonants - or consonant clusters - (generally) need to be surrounded on both sides by vowels of the same sort (i.e. leathan [a, o, u] or caol [i, e]). Some basic examples of this rule would be: 'Gaeilge', 'Teanga', 'Éire', 'uisce' and 'leathan'. The same holds true for verbs, thus: 'déanaim', 'ithim', 'cheannaigh', etc.
Language being what it is, there are obviously exceptions to this rule, but it certainly holds true for most works and is therefore a good guideline to bear in mind.
Let see, never had to write "tiomanineann" before, don't know "seisear" yet, never had to write "bantiarnai" before, never had to write 'carranna" before...so no, I didn't get this one, lol. I think I need to take a break..I have gotten onto one of those sets where they want you to write everything in Irish and my skip button is getting worn out.