4x^3-6.68E-7x^2+1.67E-8x-1.04E-10 = 0
wow. cubics are not generally easy to solve. Best bet is a graphical or numerical solution.
wolframalpha gives
http://www.wolframalpha.com/input/?i=4x^3-6.68E-7x^2%2B1.67E-8x-1.04E-10
The root is very close to zero, since
the function is very nearly 4x^3=0
Blowing up the graph a bit shows
http://www.wolframalpha.com/input/?i=4x^3-6.68E-7x^2%2B1.67E-8x-1.04E-10+for+x+%3D+-0.0004+to+0.0004