Heat And Thermodynamics

The temperature of a metal strip having coefficient of linear expansion $\alpha$ is increased from $T_1$ to $T_2$ resulting in increase of its length by $\Delta L_1$. The temperature is further increased from $T_2$ to $T_3$ such that the increase in its length is $\Delta L_2$.

Given $T_3+T_1=2 T_2$ and $T_2-T_1=\Delta T$, the value of $\Delta L_2$ is $\_\_\_\_$ .