Thu wants to play “Guess My Number.” She states, “When I triple my number and add five, I get twenty-six. What is my number?” What is her number? Show how you know.

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )