A ball is thrown straight up at 19.6 m/s…

Step 1. (a) $\dfrac{19.6\ \text{m/s}}{9.8\ \text{m/s}^2} = 2\ \text{s}$.

Step 2. (b) $\dfrac{(19.6\ \text{m/s})^2}{2 \times 9.8\ \text{m/s}^2} = 19.6\ \text{m}$.

Step 3. (c) $2\ \text{s}$ up and $2\ \text{s}$ down: $4\ \text{s}$.

Step 4. (d) $19.6\ \text{m/s}$, downward: the same speed it was thrown with.