6 radical (3) - 5 radical(12) - radical (75)
= 6 radical (3) - 5 radical(3 * 4) - radical (25 *3)
= 6 radical 3 - 5 radical(3) * radical(4) - radical (25) *radical(3)
= 6 radical 3 - 5 radical(3) * 2 - 5 *radical(3)
= 6 radical 3 - 10 radical(3) * 2 - 5 radical(3)
= -9 radical 3