Feel pretty dumb, basic trig question

If and then what is

Like I said I feel completely dumb here. I know this is so basic I'm just having a mental block with it.

Multiple choice answers are

a)

b)

c)

d)

e)

Because of the nature of the answers I know I'd have to use the unit triangle somewhere. Because tan is negative and sin is positive the answer is in quadrent 2. In other words sin1/3 = 180 - cos.

What I don't know though is how we've got the unit triangle to give sin 1/3, my stupid question is how do I get sin 1/3 on the unit triangle?