Write the following numbers in $a\ +\ bi$ form:

(a) $\displaystyle -3\left(\frac{i}{2}\right)\ =$ $+$ $i$,

(b) $(-3+i) -\ (-3+3i)\ =$ $+$ $i$,

(c) $\displaystyle \frac{5}{i}\ =$ $+$ $i$,