$$A, B, C$$ and $$D$$ are four collinear points such that $$AB = BC = CD$$. If the average velocities between $$A$$ and $$B$$, $$C$$ and $$D$$ are $$12 \text{ m/s}$$ and $$20 \text{ m/s}$$ respectively, then what is the average velocity between $$B$$ and $$C$$, if the body moves with uniform acceleration throughout?