To use the graph to find out the cost for 30 cookies you will start with the information that is given from the graph.
The easiest rate to use from the graph will be $16 for 20 cookies. If you set this up as a rate in fraction form, you can then either make a Unit rate (price per 1 cookie - see example 1 in th he attached picture) or make an equivalent rate for 10 cookies before getting to 30 - see #2 on attached picture.
The answer is $24 for 30 cookies.
