Question 989392
Make your drawing to help in assigning variables and making an equation.
I am choosing x and y for dimensions, but w for the width of the surrounding path.


Dimensions of the outer path will be  x+2w  for length and y+2w for how wide the garden.
x for garden length, y for garden's how wide.


{{{system(p=224,x=30,y=50,w=unknownOuterWidthofPathway)}}}


Only w is the unknown to solve.
Using formula for perimeter,
{{{highlight_green(2(x+2w)+2(y+2w)=p)}}}
Solve this for w.


{{{highlight(w=(p-(2x+2y))/8)}}}


Notice that this is the difference of the outer and inner perimeters, and then divided by 8.