Question 505734
t = time to build one table
c = time to build one chair
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t = 2c 
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t + 4c = 30 hr
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substitute t = 2c
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2c +4c = 30
6c = 30
c = 5
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So the time to build a chair = 5 hr to build one chair
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t = 2c
t = 2(5)
t = 10 hr to build a table
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Done.