Let $X\rightarrow Y$ be a $\mathbb{A}^n$ fibration.

If Y is affine does it imply that X is affine or quasi-affine? Is it locally trivial?

A special case: $G$ is a group. Let $H$ be a subgroup of $R_u(G)$. Then $G/H\rightarrow G/R_u(G)$ is an $R_u(G)/H$ fibration. It is well known that $R_u(G)/H=\mathbb{A}^n$. Is $G/H$ affine?