1. **Problem statement:** A projectile is launched at an angle of $30^\circ$ with an initial velocity of $20$ m/s. We need to find the time of flight. 2. **Formula used:** The time of flight $T$ for a projectile launched at an angle $\theta$ with initial velocity $v_0$ is given by: $$ T = \frac{2 v_0 \sin \theta}{g} $$ where $g = 9.8$ m/s$^2$ is the acceleration due to gravity. 3. **Calculate $\sin 30^\circ$:** $$ \sin 30^\circ = 0.5 $$ 4. **Substitute values into the formula:** $$ T = \frac{2 \times 20 \times 0.5}{9.8} = \frac{20}{9.8} \approx 2.04 \text{ seconds} $$ 5. **Interpretation:** The time of flight is approximately $2$ seconds. **Final answer:** The correct choice is (c) 2 s.