Calculate.

a) [[$ \displaystyle\frac {a} {6} \cdot \displaystyle\frac {b} {2} = $]]

b) [[$ \displaystyle\frac {1} {6} \cdot \displaystyle\frac {b} {3} \cdot \displaystyle\frac {a} {1} = $]]

c) [[$ 6 \cdot \displaystyle\frac {4} {x} = $]]