Answer
$20.2^{\circ}$.
Work Step by Step
The maxima are located by $d sin \theta = m \lambda$. The order is the value of m.
$$d=\frac{m\lambda}{sin \theta}$$
$$d=\frac{3 (700 \times10^{-9}m)}{sin 65.0^{\circ}}=2.317\times 10^{-6}m$$
Now find the angle desired.
$$d=2.317\times 10^{-6}m =\frac{2(400 \times10^{-9}m)}{sin \theta_v}$$
$$ sin \theta_v =\frac{2(400 \times10^{-9}m)}{2.317\times 10^{-6}m}=0.3453$$
$$ \theta_v =20.2^{\circ}$$
