let 'x' represent the number of hours Jane and Helen need to complete the dress together, x>0

1/x dress/hour is the together rate

Jane can sew a dress in 3 hours thus her rate is 1/3 dress/hour

Helen can sew a dress in 2 hours thus her rate is 1/2 dress/hour

1/3 + 1/2 = 1/x

by solving we find:

x = 1.2 hr

x = 1 hour 0.2*60 min

x = 1 hr 12 min

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it will take them 1 hour and 12 minutes to complete the dress together.