For a fundraiser, Marcus needs to raise $600 in order to meet his goal. Marcus will walk a certain number of miles, and he will receive donations for each mile he walks. The table represents the amount of money he has left to raise after x miles of walking.
x-2, 4, 6, 8, 10, 12
g(x) 536, 472, 408, 344, 280, 216
What is the average rate of change over the interval [6, 10]?