What are the answers to these questions?

The table above shows approximate conversions from gallons to liters. what is the value of x?

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! )

How can writing phrases as algebraic expressions you solve problems?