We can't tell from the information given. We don't know how many
different types of coins there are. All we know is that all 10 of them
on the scale at the same time have 45 grams of mass.
IF all the coins happen to be identical ... AND each one is worn down
the same amount, AND each one has the same amount of dirt and oil
on it ... then each one has (45/10) = 4.5 grams of mass.
But those are some big IFs.