Question 1079164
x, the uniform width of the flower border


total area of the yard plus flower border:  {{{(18+2x)(12+2x)}}}


Just the yard area:  {{{18*12}}}


Just the border area:   {{{18*12+60x+4x^2-18*12=4x^2+60x}}}


Area of grass-plot yard and of the surrounding border are equal.
{{{highlight_green(4x^2+60x=18*12)}}}
Solve this for the border width, x.