Please help, thank you :)

Bort wants to make money selling tacos. He sells 25 tacos on the first day. He then sells 12 tacos each day after that.

a) write an explicit formula to model this equation

b) if each taco sells for $3, how much money does he make in 30 days? Explain how you got this answer.

If you have a question, please comment, don't answer just to ask a question. Also, whoever is reading this is amazing :)