Rule 1: 1. Hearing the hidden و
In the perfect the و is visible: وَرَدَ it came in (a letter, goods), وَفَدَ he came as a delegate, وَزَنَ he weighed. In the imperfect and the jussive the word is reduced to prefix plus two radicals: يَرِدُ, يَفِدُ, يَزِنُ; لَمْ يَرِدْ, لَمْ يَصِلْ, لَمْ تَزِنْ. When such a short form puzzles you, restore the و and look for the root.
تَرِدُ الرَّسَائِلُ إِلَى الدُّكَّانِ كُلَّ صَبَاحٍ.
taridu r-rasāʾilu ila d-dukkāni kulla ṣabāḥin
Letters come in to the shop every morning.
تَرِدُ: root ورد, feminine singular agreement with a plural of things.
لَمْ تَرِدْ رِسَالَةُ التَّاجِرِ الْهِنْدِيِّ بَعْدُ.
lam tarid risālatu t-tājiri l-hindiyyi baʿdu
The Indian merchant's letter has not come in yet.
يَفِدُ التُّجَّارُ إِلَى الْمَدِينَةِ فِي مَوْسِمِ التَّمْرِ.
yafidu t-tujjāru ila l-madīnati fī mawsimi t-tamri
Merchants come to the city in the date season.
يَفِدُ from وَفَدَ; the noun وَفْدٌ 'delegation' is from the same root.
لَمْ يَزِنِ الْعَامِلُ الْأَكْيَاسَ كُلَّهَا.
lam yazini l-ʿāmilu l-akyāsa kullahā
The workman did not weigh all the sacks.
أَيْنَ نَضَعُ أَكْيَاسَ السُّكَّرِ؟ ضَعُوهَا فِي الْمَخْزَنِ.
ayna naḍaʿu akyāsa s-sukkari? ḍaʿūhā fi l-makhzani
Where do we put the sacks of sugar? Put them in the storeroom.