I would say that the best answer is actually that people who are not opposed to the new rule are less motivated to call than the people who are opposing it, who feel that they need to do something about it.
But this is not one of the options. Among the options, the best is: A. The survey is voluntary and includes only listeners of this radio program.
So I guess you man 15% raise! 2100×0.15=315 now that's the actual increase in pay so what he actually gets it 2100+315=2415 dollars per month more than previous month's