Question 1130834
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The number of rows is 3x and the number of trees in each row is 2x, according to the condition,

where x is the common measure (now unknown) of these two numbers.


In addition, we know that the total number of threes in the garden is 864:


    (3x)*(2x) = 864.


It gives you 


     6x^2 = 864

     x^2 = 864/6 = 144  ====>  x = {{{sqrt(144)}}} = 12.


Thus the length of each row is 7*(2x) = 7*2*12 = 168 yards.


The other dimension of the garden is  7*(3x) = 7*3*12 = 252 yards.


You may want to add a uniform strip around this rectangle of 7/2 = 3.5 yards wide.


It depends on conditions that are not defined clearly and explicitly in the problem, so I leave it up to you.
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