From the top of a building 40 m tall, a ball a thrown vertically upwards with a velocity of $10\; ms^{-1}$ After how long will the ball hit the ground?

Question

$\begin{array}{1 1} 4s \\ 3s \\ 2s \\7s\end{array}$

Comments

2 sec is the right answer

---

which is the right answer 2 or 4?