It should be
The education minister has come under fire over a five-fold increase in three years in the number of students ----
five should be fire.
This looks like an incomplete sentence - under fire for REASON and the REASON part looks incomplete
Under fire - this means that someone has criticised him either in the media or in the elected assembly. Under fire can also be replaced by "has been attacked".
It does not mean a literal fire or a literal attack. It just means criticism.