Question 418812
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Hi
A 20 foot board
Let x and (20-x)represent the longer ans shorter piece respectively
Question Sets Up the Proportion
  {{{ 7/3 = x/(20-x)}}}    |Cross Multiplying 
    3x = 7(20-x)
   10x = 140
     x = 14ft, the longer board

CHECKING our Answer***
  14/6 = 7/3