It is around 17 and 3 but it gets to close at that point but I was able to get down to 2.95 and 17.05
The given plane, 
, has normal vector 
. Any plane parallel to this one has the same normal vector.
Let 
be any point in the plane we want. The plane contains the point (1, 1, -1), so an arbitrary vector in this plane is
and this is perpendicular to 
.
So the equation of the plane is
or equivalently,
Hzhsususuhhhdhdhhddhdhhdjxxj
Lets say w is the width of the flower bed. We can make an equation to find the area.
The length of the of the flower bed is (w+5) and the width is w.
To find the area we need to multiply the length(w+5) by the width(w) and set it equal to 84,
(w+5)(w)=84
w^2 +5w=84
Using the quadratic equation you get the solutions of 7 and -12. Since 7 is positive it is our width. Our length is 7+5 or 12.
