Okay, here is how we get to 3.8c.
USD $2.5mil = AUD $3.45mil at spot prices which are most relevant here.
AUD $3,450,000 ÷ 90,672,814 = 0.03805c = 3.8c
I think it's reasonable to assume that the AUD $500,000 payment must have related to interest or some other term of the note.