At Think Olympics, Francis completes an $$1200-$$meter race. He runs the first $$420$$ meters at a speed of $$7$$ meters per second, the middle $$620$$ meters at a speed of $$5$$ meters per second, and in the sprint stage, Francis runs at a speed of $$8$$ meters per second. Find the time Francis spends on the entire race (in seconds). 
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