alfred has twelve coins in his piggy bank. some of the coins are quarters, some are nickels, and he has a total of $3.15. which system of equations can be used to determine how many quarters, x, and how many nickels, y, he has

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 (%)