If there are 4 equal sections of a 28ft fence, 28/4 = 7ft per section. If you've painted 1/2 of 1 section, you've painted 7*1/2 or 3.5ft. Then find what fraction 3.5 is of the total, 28.
3.5/28 = 0.125 or 1/8 of the job
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