Jack collected 360 ships models 40% of them were made by him. If Jack donated 25% of models which he made and donated 50 of models he bought how many fewer models made by himself were donated than those he bought

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 (%)