Three equal weights of 3 ~kg each are hanging on a string passing...

Three equal weights of $3 \mathrm{~kg}$ each are hanging on a string passing over a pulley as shown in figure. If $a$ is the common acceleration. $T-3 g=3 a$ (For mass I) $3 g+T_1-T=3 a$ (For mass II) $3 g-T_1=3 a$ (For mass III) Adding, above three equations $$\begin{aligned} & 3 g=9 a, a=g / 3 \\ & T_1=3 g-3 a=3 g-g=2 g=20 \mathrm{~N}\end{aligned}$$