Mary has 39 square feet of patio bricks. each square brick has sides 1 foot long. what is the greatest perimeter of a rectangle that she can make with bricks

-- The smallest perimeter you can make with a certain area
is a circle.

-- The NEXT smallest perimeter with the same area is a square.

   With 1-ft by 1-ft square bricks, the shortest perimeter she could
make would be by using her bricks to make it as square as possible. 
Without cutting bricks into pieces, the best she could do would be  

                           (13 bricks) x (3 bricks) .

                            =    (13-ft) x (3-ft)

           Perimeter = (2 x length) + (2 x width)

                             = (2 x 13-ft)  +  (2 x 3-ft) 
                           
                             =      (26-ft)  +  (6-ft)  =  32 feet  <== shortest perimeter.

-- Then, the more UNSQUARE you make it, the more perimeter
it takes to enclose the same area.  That means Mary has to make
a rectangle as long and skinny as she can.

The longest perimeter she can make (without cutting bricks into
pieces) is    (39 bricks) x (1 brick) .

                        = (39-ft)  x  (1-ft) .

    Perimeter  =  (2 x length) + (2 x width)

                       =   (2 x 39-ft)  +  (2 x 1-ft)

                       =        (78-ft)  +  (2-ft)     =     80 feet .    

What she'll have then is a brick path, 39 feet long and 1 foot wide,
and when you walk on it, you'll need to try hard to avoid falling off
because it's only 1 foot wide.