Did it take longer to go from 6 - 7 million units sold, or from 7 - 8 million units sold?
return to go from  6 -  7  million  units sold ;return to go from  7  -  8 million  units sold ;return how long was  #1 ;return how long was  #2 ;return which is the  highest of #3 ,  #4
['select', 'select', 'project', 'project', 'comparison']