Rashi on Leviticus 27:19/רש"י על ויקרא כ״ז:י״ט

1ואם גאל יגאל AND IF HE WILL IN ANY WAY REDEEM IT “he” means, the man who dedicated it; then he shall add a fifth part to this fixed price (not a fifth of the fifty shekels, but a fifth of the value determined by this calculation is to be added to that value).