Question 42285
It can be solved but I am not complete sure how to do it.  What is there is almost correct because the complete area of the garden minus the are of the path would be equal to the remainder of the garden.  If you were to draw the garden out with path included you would see that the width would be the same for both path and garden however the length would be shorter for the path then the whole garden by 2x since the path is uniform.
{{{400=(30*20)-(20(30-2x))}}}
{{{400=(600)-(600-40x)}}}
{{{400=600-600+40x}}}
{{{400=40x}}}
{{{x=10}}} so the width of the path is 10 feet.