How would this question be answered using the SUMPRODUCT format
in excel?

Each year, a shoe manufacturing company faces demands (which
must be met on time) for pairs of
shoes as shown in the table below.
Quarter 1 Quarter 2 Quarter 3 Quarter 4
Demand 6000 3000 8000 1000
Employees work three consecutive quarters and then receive one
quarter off. For example, a worker
might work during quarters 3 and 4 of one year and quarter 1 of the
next year. During a quarter in
which an employee works, he or she can produce up to 500 pairs of
shoes. Each worker is paid £5000
per quarter. At the end of each quarter, a holding cost of £10 per
pair of shoes is incurred.
a) Formulate algebraically a linear programme to minimise the cost
per year (labour plus holding) of
meeting the demands for shoes. To simplify the model, assume that
at the end of each year, the
ending inventory is 0. (You can assume that a given worker gets the
same quarter off during each
year.)