Answer: a) $17, b)
![12+0.50s](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9ukynzrcx6f81i2y88q9cw1edm3f0z8axv.png)
Explanation:
Since we have given that
Cost per month = $12
Cost per song = $0.50
Number of songs downloaded = 20
According to question, we get that
![12+0.50* 10\\\\=12+5\\\\=17](https://img.qammunity.org/2020/formulas/mathematics/middle-school/99esyp3xn8syqr4zxxo9uyjc53l7dx763a.png)
She has to pay $17 if she downloaded 20 songs.
If the number of songs = s
So, Amount she has to pay is given by
![12+0.50s](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9ukynzrcx6f81i2y88q9cw1edm3f0z8axv.png)
Hence, a) $17, b)
![12+0.50s](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9ukynzrcx6f81i2y88q9cw1edm3f0z8axv.png)