Answer:
a = (v₃₂ - v₂₁) / (t₃₂ -t₂₁)
Explanation:
This is an exercise of average speed, which is defined with the variation of the distance in the unit of time
v = (y₃ - y₂) / (t₃-t₂)
the midpoint of a magnitude is the sum of the magnitude between 2
t_mid = (t₂ + t₃) / 2
the same reasoning is used for the mean acceleration
a = (v_f - v₀) / (t_f - t₀)
in our case
a = (v₃₂ - v₂₁) / (t₃₂ -t₂₁)