Let \( y = y(x) \) be the solution of the differential equation \( (x^2+1)\,y' - 2xy = (x^4 + 2x^2 + 1)\cos x, \; y(0)=1 \).Then \(\displaystyle \int_{-3}^{3} y(x)\,dx \) is:
\(36\)
\(24\)
\(30\)
\(18\)