That would mean that the average field worker would have to harvest 100 heads of lettuce every hour to make $3.00. To get to $15.00 per hour, he would have to harvest and pack 500 heads of lettuce every hour and roughly 5000 heads every day.
I think your math is a little fuzzy.
picking and packing it is not the only labor involved, it has to be planted and taken care of for months and months
$0.03 X 500 heads/hour = $15.00/hour. That works out to about 10 heads per minute or one head every 6 seconds.