EDIT: SHINY PICTURE NOW:

After this, I can't be bothered learning latex, pretend x1 and x2 are theta 1 and 2

From this, we can see x1+x2 = 90º => x2=90-x1

Using our mate snell's law as per normal, 1 sin x1 = 1.33 sin x2

sin x1 = 1.33 sin (90-x1)

sin x1 = 1.33 cos x1

tan x1 = 1.33

x1 = 53º

Edit: Today when studying for my exam at 2:30 I learnt of Brewsters Law, which says if the reflected and refracted rays are perpendicular, then theta = arctan(n_2/n_1)

Which is essentially what I derived by doing arctan(1.33/1)