Question 1182600
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Your equation is 


    L*(L-3) = 70.


Simplify and reduce it to the standard form of a quadratic equation.


Then solve it using the quadratic formula or factoring (both work in this case).


<U>ANSWER</U>.  The length is 10 inches.
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Also, you may guess the answer mentally without using any equation/equations.


Since the left side of the equation is monotonically increasing function of the length L,

the guessed solution is UNIQUE: there is NO another solution.