Ijust need the advance ticket price iknow that the same day is 15$ suppose that there are two types of tickets to a show: advance and same-day. the combined cost of one advance ticket and one same-day ticket is 35 . for one performance, 15 advance tickets and 40 same-day tickets were sold. the total amount paid for the tickets was 900 . what was the price of each kind of ticket?

I would feel better if you'd explain how you "know" that a "same-day" ticket is $15.  

"The combined cost of one advance ticket and one same-day ticket is $35."  This would imply that the cost of one advance ticket is $(35-15), or $10.  

Check by substitution to determine whether $15 and $10 are correct.  If not, please show your work, so that someone else or I could step back in and help.

Yea they are simplyfiy the ratios