Understanding the Concept of a Limit

Need on this one asap im almost done with this subject

Based on the figures as marked, /\rqs = —

Acompany that manufactures and sells guitars made changes in their product range. from the start they had 20 models. then they reduced the number of models to 15. as a result, the company enjoyed a 10% increase in turnover. - how much did the stock level change? in (%)