physics word problem (help pls)

Question

 While on vacation, Raul is staying in a hotel room with a balcony 18.0 m above the ground that is overlooking the ocean. He is curious as to how far he could throw a rock before it hit the water. Recognizing that it would be unsafe to actually throw the rock, he decides to work out the answer mathematically. He knows that he can throw the rock horizontally at a speed of 30.0 m/s. How far from the hotel will the rock be when it hits the water?

Answer 1

 While on vacation, Raul is staying in a hotel room with a balcony 18.0 m above the ground that is overlooking the ocean. He is curious as to how far he could throw a rock before it hit the water. Recognizing that it would be unsafe to actually throw the rock, he decides to work out the answer mathematically. He knows that he can throw the rock horizontally at a speed of 30.0 m/s. How far from the hotel will the rock be when it hits the water?

y = ½ g t² + v₀ t + y₀ but v₀ = 0 in y direction. So y = ½ g t² + y₀.

y - y₀ = ½ g t², t = √( 2 (y-y₀)/g ) = √( 2(0 m -18.0 m)/(-9.81 m/s²) ) = 1.9 s

x = v t = (30.0 m/s)(1.9 s) = 57 m

Let me know if I can explain any parts of this more clearly. Thank you!