Physics problems?

I solved number 5. I just need help with number 3 now..

(a)$Snell's$ $Law$: $n$_$1$$sin(\theta$_$1$$)=n$_$2$$sin(\theta$_$2$$)$

n₁=1

n₂=1.33

(b) $\theta$₁ =$\theta$₃=40º

$\theta$₂=?

sin(40)=1.33sin($\theta$₂)

$\theta$₂=arcsin[100sin(40)/133]

$\theta$₂=28.90º

(c) f=speed of light in substance

c=speed of light in vacuum=3*$10^8$m/s

n=index of refraction

$f={c\over n}$

f=3.99*$10^8$m/s

(d) h=frequency

w=wavelength

f=speed of light in substance

f=hw

3.99*$10^8$m/s=7.85*10¹⁶/s*w

w=(3.99/7.85)*(10^8-16)=5.08*10^-9m

(e) $Snell's$ $Law$: $n$_$1$$sin(\theta$_$1$$)=n$_$2$$sin(\theta$_$2$$)$

n₁sin($\theta$₁)=1

sin(90)=1

1.33sin($\theta$₂)=1

$\theta$₂=arcsin(100/133)=48.75º