Plz help me to solve this question.

This is of Profit loss and simple interest.
Answer is Rs 20 each.
I want full process.
I will mark you brainlist if you write the full process.

A shopkeeper bought 1000 glass tumblers. 100 of them were broken and he sold the remaining tumblers at Rs21 each. If he made a loss of 5.5 %, at what purchase each glass tumblers​