Based on the vertex and table this is the graph.
Price per hour of first case :
( Here, a is number of hours )
Price per hour of second case :
( Here, b is number of hours )
Let, after x hours both company charges the same.
Hence, this is the required solution.
Sydney has 10 because 30 is 3 times as many as 10 and then the extra 6 is the one you added when it says 6 more than three times