From $\large\frac{3}{4}+\frac{1}{2}\;$$i$ subtract its complex conjugate . What is the difference ?

Question

$\begin{array}{1 1} (a)\;i \\ (b)\;-i \\ (c)\;-\large\frac{1}{2} \\(d)\;\large\frac{1}{2}i \end{array}$