From a hot-air balloon hovering 64 m above a field, a man drops ball A…

Step 1. Meeting time. $\dfrac{64\ \text{m}}{20\ \text{m/s}} = 3.2\ \text{s}$.

Step 2. Height. A has fallen $4.9\ \text{m/s}^2 \times (3.2\ \text{s})^2 = 50.2\ \text{m}$, so it is $64\ \text{m} - 50.2\ \text{m} = 13.8\ \text{m}$ up.

Step 3. Ball B's velocity. $20\ \text{m/s} - 9.8\ \text{m/s}^2 \times 3.2\ \text{s} = -11.4\ \text{m/s}$: B is already falling.