Hey, i don't know how long ago this questions from but
the answer 19 is right!
This is how you do it:
the formula as you said is
n_1 \sin \theta _1 = n_2 \sin \theta_2
what you do is
n_1(1) \sin ( 65 = n_2(1.55) \sin \theta_2
and then you get
Sin(65) divided by 1.55 = refractive...