9,15 it that equivalent

Convert 16 yards to feet use the conversion rate 3 feet = 1 yard

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 (%)

Can someone me out here number 4 plz