Information given
The perimeter of a triangle is 49 ft
And let's the 3 sides of the triangle A, B and C. From the info given we know:

And we also know some conditions given by: (Side B is 3 ft shorter than A)

Side C is twice the lenght of A:

Now we can replace in the first equation the conditions and we have:

Now we can do some algebra:



The only possibility that makes sense from the options given is:
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