One way to approach this would be to express 125^2 as (125)(125).
Note also that 125^(4^3) = 125^(1 + 1/3) = (125)(5)
Therefore, the given expression boils down to
(125)(125) 125
--------------- = ------- = 25
5 (125) 5
There are other ways in which you could reduce the given expression.
