Shows two ways five people can share a 3 segments chewy fruit worm

Which expression can be used to determine the slope of the line that passes through the points -6, three and one, -9

The price of an item has been reduced by 30%. the original price was $30. what is the price of the item now ?

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! )