Answer:
 ∆GHE ~ ∆FHG ~ ∆FGE
 HF = 16
Explanation:
The similar triangles can be identified this way.
 ∆GHE ~ ∆FHG ~ ∆FGE
Then the proportion involving sides FE, FH, FG can be written as ...
 FG/FE = FH/FG
 FH = FG²/FE . . . . . . . multiply by FG
 FH = 20²/25 . . . . . substitute given values
 FH = 16
The length of HF is 16 units.