I have a question involving optimal consumption bundles for quasi-linear preferences. Utility is given by
$$U(x_1,x_2) = 16\sqrt{x_1} + 2x_2$$
and $p_1 = 8, p_2 = 4, I = 30$.
What I have so far is
$$8x_1 + 4x_2 = 30$$ and
$$MRS = -\frac{4}{\sqrt{x_1}} = -\frac{p_1}{p_2} = -2$$
Solving that I get $x_1 = 4$, but plugging that into the budget equation results in a negative value for $x_2$. What am I doing wrong here?