Answer:
1.3m/s²
Step-by-step explanation:
Given values in the first part: acceleration a, time t₁:
1) velocity v₀
2) height h₀
Given values in the second part: acceleration -g, time t₂:
3) height h
Combining equations 1,2,3 and setting h to zero:
Solve for a with t₁ = 4s and t₂=2.1s: