Find the surface of the figure : 1ft ,5ft,7ft

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 with the property questions for 12 13 and 14 plz

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)