Help me plz if you can

Which ordered pair (c, d) is a solution to the given system of linear equations- c+2d=13 -9c-4d=-15

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 (%)

Which number completes the inequality? 2/3 < _ < 7/9