You mean "10,000 for 60cm, 2,000 for 40cm and 4,000 for 20cm? in the list"?
If so read on:
What to product depends on the product which has the highest contribution per limiting factor.
In this quesiton it is a choice between 20, 40 60cm.
The mark scheme does not really highlight the "ranking" / ordering of the better size to produce but is in order in the list 60cm then 40 then 20 due to higher contribution per labout hour (which is the limiting factor).
Contribution per labour hour £19 for £60 so make as many as possible. i.e. the full 10,000 units (see demand for pots in question). This takes 60 minutes / 1 hour per pot so is 10,000 hours used of the 13,500 direct labout hours available (see additional information (3)). Then 40cm is £17.33, the 2nd best so make the 2,000 units at 45 minutes per unit / 3/4 of 1 hour this taking 1,500 hours.
Total hours so far is 10,000 + 1,500 = 11,500 so take that away from max of 13,500 gives 2,000 hours spare for 20cm and work out how many units this would product. i.e. it takes 30 minutes / 1/2 an hour so they can produce 4,000 units i.e. 2,000 / 1/2.
Hope this is useful. Students tend to forget to turn the minutes into fractions of hours to correctly work out.