Answer
$0.354mm$
Work Step by Step
We know that
$\frac{m_tx_t+m_wX_{CM}}{m_t+m_w}=0$
This simplifies to:
$X_{CM}=\frac{-m_tx_t}{m_w}$
We plug in the known values to obtain:
$X_{CM}=-\frac{0.0502Kg}{35.5Kg}(25cm)$
$X_{CM}=-0.03535cm$
Since the distance is positive:
$X_{CM}=0.03535cm=0.354mm$
