Answer
$31Kg$
Work Step by Step
According to law of conservation of momentum
$p_1x+p_2x=0$
$\implies m_1v_1x+m_2v_2x=0$
This can be rearranged as:
$m_2=\frac{-m_1v_1x}{v_2x}$
We plug in the known values to obtain:
$m_2=\frac{-(45)(-0.62)}{0.89}$
$m_2=31Kg$
