Find the equation of normal for the parabola $y^2=4ax$ in parametric form

Question

$\begin{array}{1 1}(a)\;y+x=2at+at^3\\(b)\;y^2+x^2=2at+at^3\\(c)\;y+x=at+at^2\\(d)\;y+2x=at+at^3\end{array}$