On 13- a, b, ccan anyone tell me if the ones i did are right

Place the following steps in order to complete the square and solve the quadratic equation,

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 (%)

Why is x= 4 a solution to the proportion 14/x 56/1 6