Y=23x y=-x+5y=−x+5 pls help

If a baby uses 15 diapers in 2 days how many diapers will the baby use in a year

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! )

What is the gcf of 20c^3-5c^4+30c^6