Option a:
is the length of b
Explanation:
The angle of B is
and 
We need to determine the length of b.
First, let us determine the angle of A.
Since, ABC is a triangle, then all the angles add up to 180°
Thus, we have,




Thus, the angle of A is 
Now, we shall determine the length of b using the sine law formula.
The formula for sine law is given by,

where
,
, 
Thus, we have,

Simplifying, we get,

Multiplying both sides by 0.866, we get,

Multiplying the numerator, we have,

Dividing, we get,

Thus, the length of b is 
Hence, Option a is the correct answer.