Final answer:
Isabella's music service bill increases at a rate of $1.31 per song downloaded. This was calculated by comparing two instances of her monthly music expenses for different numbers of downloaded songs and finding the constant rate.
Step-by-step explanation:
The student is asking to calculate the rate at which Isabella's bill increases per song download on the online music service she uses. Given are two instances – in one month, she downloads 11 songs and pays $19.40, and in the next month, she downloads 16 songs and pays $25.95. We can set up two equations based on the information provided:
- For 11 songs: Monthly fee + (11 × per-song rate) = $19.40
- For 16 songs: Monthly fee + (16 × per-song rate) = $25.95
We then calculate the increase in cost for the increase in songs, which represents 5 more songs and $6.55 more in cost. Dividing the increase in cost by the number of additional songs gives us the per-song rate:
Per-song rate = $6.55 / 5 songs = $1.31 per song.
Therefore, the answer is A. $1.31, which is the rate at which Isabella's bill changes with respect to the number of song downloads.