to find all of the roots, you must know that the roots are the intercept with the x-axis. (y=0)
One solution would be x^2 + 0.15861...x-16.29207...~0
x~+4.11643...~0
x~-4.11643...
The final solution is
x~-1.84139...,x~3.95782...,x~-4.11643...
I hope this helped you.