Question 990983
x, the edge length of the square removed at each corner;
The area of the base is  {{{(30-2x)(58-2x)}}};
Area of the four sides other than the base, {{{2x(30-2x)+2x(58-2x)}}};


The total area is given.
{{{highlight_green((30-2x)(58-2x)+2x(30-2x)+2x(58-2x)=348)}}}
A quadratic equation needing simplification steps and then solve for x.