How many more of the percentage of the class was employed by nine months after graduation than secured positions in one of 250 largest firms?
return class that was employed by nine months after graduation ;return class that secured positions in one of the 250 largest firms ;return percentage of #1 ;return percentage of #2 ;return the difference of #3 and #4
['select', 'select', 'project', 'project', 'arithmetic']