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3.

Area   =  pi * r^2   ....so  we have

108.94  =  pi * r^2      divide both sides by pi

108.94 / pi  = r^2      take the square root of both sides

√ [ 108.94 / pi ]  =  r  ≈  5.89 ft 

4.  Note, NSS....we don't need to do much math here....logic will suffice

From  a  positive radical on the right, we CANNOT  get a negative answer....thus....the 5x  on the left side CANNOT evaluate to a negative whenever we plug in  an x value.....thus, x CANNOT be negative

Notice that the first, second and fourth answers will produce at least one negative outcome for 5x

So....by a process of elimination, the second answer is the only one that is any good

Do you see that???.....sometimes....logic is BETTER than MATH  !!!