The blank requires a clause using 'could' to express an unreal or hypothetical situation, as indicated by the brackets. Following the pattern from the text ('I wish I could be...'), 'could' is used here to express a wish that is contrary to present reality. Using the context of the passage, where people wished to finish secondary school but had to work instead, 'I could finish secondary school' fits perfectly as a hypothetical wish to do something without worrying about money.