Need help with this question.

Ben wants to play a carnival game that costs $2. in his pocket he has 5 red tickets worth 35 cents each, and 15 blue tickets worth 10 cents each. which of the following systems of inequalities correctly represents the constraints on the variables in this problem? let represent the red tickets and b represent the blue tickets.

Sole the equation 6n + 9 = -3n - 21 - 6 for n

Could you show the work on how u got this so i could understand?