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Eva and Sophia rent a booth at a local market every Sunday and sell T-shirts. 
It cost them $20  to make  EACH  shirt and $400 to rent at the booth. 
If they sell shirts for $30 each what is their break even point?
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    30x = 20x + 400   dollars.
    30x - 20x = 400
        10x = 400
          x = 400/10 = 40  T-shirts.    ANSWER
Solved.
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