The cost to purchase a song from iTunes is $0.99 per song. To purchase a song from Napster, you must be a member. The Napster membership fee is $10. In addition, each purchased song costs $0.89. How many downloaded songs, d, must be purchased for the monthly price of Napster to be the same as iTunes?
This problem has a very easy solution, I'll give you a hint, solve the equation:
0.99d = 0.89d + 10
Once you get d, that's your answer