Solution
= Solution
For the quartic potential,
$$
\frac{V}{V'}=\frac{\phi}{4}.
$$
Integrating the result of part (c) along the trajectory from $\phi_i$ to $\phi_f$ gives
$$
N\simeq-8\pi G\int_{\phi_i}^{\phi_f}\frac{\phi}{4}\,d\phi
=\boxed{\pi G(\phi_i^2-\phi_f^2)}.
$$
Because the negative field rolls toward zero, $\phi_i<\phi_f<0$ and $|\phi_i|>|\phi_f|$, so this <monomial slow-roll e-fold count> is positive.