Translation:The mango fell
The subject prefix i- is used for noun class 4 (the Mi in the M/Mi pair) and noun class 9 (singular N in N/N).
Prefix li- is used for class 5 (Ji). If this sentence was "the mangoes fell" the prefix would be ya- and the sentence would read maembe yalianguka.
If you've already passed Object Infix (judging from the sentence I'm guessing you're at Stative Verbs), go onto the website and carefully read the tips & notes. The list of infixes for each class is the same as their subject prefix (with exceptions in M/Wa class). I suggest writing them out somewhere and referring back to them as necessary.