How is the phrase 'Four months and ten' to be interpreted in the context of the waiting period ('iddah)?

Primary text

The 'ten' does not refer to ten months. This is established for two reasons: First, the word 'ashar' (ten) without the feminine marker (taa marbuta) is used to count feminine nouns, but 'ashhur' (months) is masculine, making the construction linguistically impermissible. Second, if it meant ten months, the structure would be 'fourteen months' (using compounding) rather than structured by conjunction (wa/and), as seen in Quran 50:17 ('nine').