Answer:
So, we purchased 9 songs and 4 games for 20.1$.
So, we purchased 10 songs and 6 games for 25.5$.
So, we purchased 10 songs and 10 games for 33.9$.
Explanation:
We have receive a $35 gift certificate from an online retailer that sells digital music and games. Each song costs $1.29 and each game costs $2.10.
First case:

So, we purchased 9 songs and 4 games for 20.1$. We have 13 items for 20.1$.
Second case:

So, we purchased 10 songs and 6 games for 25.5$. We have 16 items for 25.5$.
Third case:

So, we purchased 10 songs and 10 games for 33.9$. We have 20 items for 33.9$.