The first thing we do is find the unit rate. To find the unit rate you will divide $5 by 6 to figure out the cost of 1 orange. Five divided by 6 equals about 0.83. This lets us know that 1 orange cost about $.83, which is our unit rate. Since we know the unit rate, we'll multiple .83 by 18 to get the cost of 18 oranges. .83 multiplied by 18 equals 14.94. So 18 oranges will cost $14.94 or if rounded up about $15. Since 15 is the closest to 14.94 we can assume that the answer is C.