Question 299128
Since you say nothing about the height of the box, we'll let h = the height.
The volume, V of such a box can be expressed by:
{{{V = hx^2}}} and this is given as 50 cubic feet so...
{{{50 = hx^2}}} or {{{x^2 = 50/h}}}
The surface area of the box {{{A}}} will define how much material is required to fabricate the box.
The box will have four equal faces (sides) and a top & bottom (both equal) for a total of six faces.
We need to determine the area of each of these face and then find their sum to obtain the total surface area and, thus, the amount of material (A) required to fabricate the box.
The top and bottom surfaces will each measure x times x for  a total surface area of {{{2x^2}}}sq.ft..
The four equal faces will each measure x times h for a total surface area of {{{4hx}}}, so the sum of these is:
{{{A = 2x^2+4hx}}}sq.ft.
Now if the box is really a cube and {{{h = x}}}, then...
{{{A = 6x^2}}}sq.ft.