In the two systems as shown, the value of mass M so that extensions in two springs (of same spring constant k) is same ___________(in kg)?

For I^st diagram  $T_1=\frac{m_1{m}_{2}g}{m_1+m_2}=\frac{2\times 3}{2+3}g=\frac{6g}{5}$

For II^nd diagram  $T_2=\frac{m_1{m}_{2}g}{m_1+m_2}==\frac{4M}{4+M}g$

$T_1=T_2\Rightarrow \frac{6g}{5}=\left(\frac{4M}{4+M}\right)g$

$6\left(4+M\right)=20M\Rightarrow 24+6M=20M$

$14M=24\Rightarrow M=\frac{24}{14}=\frac{12}{7}=1.71$kg