I need this question put into an equation. I have been working on this forever and cannot figure out! Please explain what you did. Thanks so much for your time!

Mark sold 105 tickets for the basketball game. Each adults ticket cost $2.50 and each child's ticket cost $1.10. Mark collected $221.90. How many of each kind of ticket did he sell?

Let

number of adult tickets sold = A
Cost of each adult ticket = 2.50
Total cost of adult tickets = 2.50*A

number of child tickets sold = C = 105-A
Cost of each child ticket = 1.10
Total cost of child tickets = (105-A)*1.10

Total cost of all tickets=
2.50A + 1.10(105-A) = 221.90