The revenue in the first year is 5160, so the working capital at the start of the first year (i.e. time 0) is 20% x 5160 = 1032.
The revenue in the second year is 24883, which is 19723 higher than that in the first year. So (as per the relevant paragraph in the question) the extra working capital needed is 10% x 19723 = 1972.
The same logic applies in the later years (except that in the final year all of the working capital is recovered as again per the instructions in the question).