Khushi & her dresses

Khushi has $x$ dresses in her wardrobe. She leaves for college in the morning at 8:00 AM and wears a new dress each day. When she is back home, She takes shower and gives her dress to her mother for charity. Her mother doesn't like her habit and decides : 1. To buy a new dress for her every $yth$ day **(i.e. y, 2y, 3y)** instead of buying one every day. 2. She will bring the dress late at night