Getting confused?

A particle moves in three consecutive time periods $t_1, t_2,$ and $t_3$ seconds with constant acceleration. If the average velocities in the three periods are $v_1=5\text{ m/s},\quad v_2=8\text{ m/s},\quad v_3=12\text{ m/s},$ respectively, then find the value of $\frac{t_1 + t_2}{t_2 + t_3}$ .

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Note: $t_1, t_2,$ and $t_3$ are distinct positive numbers.