The examiner has taken the net current assets of 270 and subtracted the cash of 50 (in note 6 of the question) in order to arrive at working capital of 220. However he does write in his answer that you could have used the full 270 are the working capital and that using either would get full marks.
Note 2 of the question sats that the investment in working capital will increase in lone with the growth in gross profit, which from note 4 is 9%.