What is the used (kb) when the graphics mode is 4?
{'header': ['Graphics mode', 'Char cells', 'Pixels', 'Hardware colours', 'used (KB)', 'map', 'Type'], 'page_title': '', 'section_title': '', 'caption': '', 'rows': [['0', '80 × 32', '640 × 256', '2', '20', '3000–7FFF', 'Graphics'], ['1', '40 × 32', '320 × 256', '4', '20', '3000–7FFF', 'Graphics'], ['2', '20 × 32', '160 × 256', '8', '20', '3000–7FFF', 'Graphics'], ['3', '80 × 25', '640 × 200', '2', '16', '4000–7FFF', 'Text'], ['4', '40 × 32', '320 × 256', '2', '10', '5800–7FFF', 'Graphics'], ['5', '20 × 32', '160 × 256', '4', '10', '5800–7FFF', 'Graphics'], ['6', '40 × 25', '320 × 200', '2', '8', '6000–7FFF', 'Text']]}