1. h₀ = 70
v₀ = 0 since the rock is dropped it has no initial velocity
when the rock hits the ground the height = 0
plug into the formula
0 = -4.9t² + 0(t) + 70
0 = -4.9t² + 70
Add 4.9t² to both sides
4.9t² = 70
Divide both sides by 4.9
t² = 14.2857142857
Take the square root of both sides
t = 3.7796447301
t ≈ 3.8 seconds
I am not doing the rest I only did one just to help you understand a bit more