7workers can make 210 pairs of cup in 6 days. how many workers are required to make 450 pairs of cup in 10 days?

9 workers
7 workers can make 210 pairs of cup in 6 days, so:
1 worker can make 30 pairs of cup in 6 days, so:
1 worker can make 5 pairs of cup in 1 day.
Using this info, because
the workers need to make 450 pairs of cup in 10 days,
they need to make 45 pairs of cup in 1 day,
each worker can make 5 pairs of cup in 1 day, 

so 45/5 = 9 workers
voila!

The correct answer is b, social stratification is needed for a society to exist. marxist theory regarding social stratification is that due to the differing economic capacities among people in society, a natural separation occurs between those that own the means of production and those that sell their labour in the production chain.