Question 973550
You said not how you assigned x, but you may have dimensions x and y for the rectangular cardboard.


Make a drawing and assign some variables, and label the drawing based on these:


A = 304, the area of the cardboard before cutting and folding
d = 2, the side length of the square to remove from each corner
v = 360, the volume of the finished box


FORMULATE EQUATIONS


{{{xy=A}}} ----------- to account for original rectangle area
{{{(x-2d)(y-2d)d=v}}} ---------- accounting for finished box volume


Those are two equations in two unknown variables.  You already have KNOWN values for A, d, and v.  You will be able to form a quadratic equation in either x or y, and solve for the variable.  Again, notice I say, "QUADRATIC"; and not cubic.  Try to work completely in symbols for as far as you can; before finally substituting the given values to evaluate x and y.


First step should be like, y=A/x,  and substitute this into the v equation, and simplify... that is really more than "first step".