At Think Olympics, Jack completes an $$800-$$metre race. He runs the first $$280$$ metres at a speed of $$7$$ metres per second, the middle $$400$$ metres at a speed of $$5$$ metres per second, and in the final sprint stage, Jack runs at a speed of $$8$$ metres per second. How long did Jack take to finish the entire race (in seconds)? 
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