The final 4 is in the numerator, not the denominator.
5² × 4 × 5 × 4² / 5 (4)
= 25 × 4 × 5 × 16 / 5 × 4 . . . . . exponents are computed first
= 100 × 5 × 16 / 5 × 4 . . . . . . . multiplication and division left to right in order
= 500 × 16 / 5 × 4
= 8000 / 5 × 4
= 1600 × 4
= 6400
