Maths Questions - Transportation Problem

This is done in excel. Some help on where to start would be nice.

A computer manufacturer has four factories A, B, C and D which produce in order 500, 250, 300 and 600 computers per week. The computers are transported to be stored in 5 warehouses W1, W2, W3, W4 and W5 which can accomodate in order 200, 150, 300, 600 and 400 computers.
Subsequently the computers are sent on to shops for sale. The transport costs per computer are
given as below.
a) Manually fill in the number of computers transported in the top table to get an initial cost.
b) Try to change your initial attempt in a) to reduce the overall costs.
c) Use the excel solver to get a solution to the costs. Comment briefly on your answers to a), b)
and c).
d) Comment briefly on any practical difficulties that the above problem may encounter.

Can you apply the north-west corner method to obtain an initial solution? You know the supply of each factory and the demand of each warehouse so this is enough information.

Pictures would be helpful when done

Thanks for the reply but i got help elsewhere and have finished it now but thanks anyway. p.s. i have no idea what the n-w corner method even is.