Here is a double number line showing that it costs $3 to buy 2 bags of rice: A double number line with 6 evenly spaced tick marks. The top number line is labeled "cost, in dollars." The number 0 is indicated on the first tick mark and 3 is on the second. The bottom number line is labeled "rice, number of bags." The number 0 is indicated on the first tick mark and 2 is on the second. At this rate, how many bags of rice can you buy with $12? Find the cost per bag. How much do 20 bags of rice cost?