Answer
$Ca_3P_2(s)+6H_2O(l)\rightarrow 3Ca(OH)_2(aq)+2PH_3(g)$
Work Step by Step
$Ca_3P_2(s)+H_2O(l)\rightarrow Ca(OH)_2(aq)+PH_3(g)$
Add a coefficient of 3 to $Ca(OH)_2$ to balance $Ca$.
Add a coefficient of 2 to $PH_3$ to balance $P$.
$Ca_3P_2(s)+H_2O(l)\rightarrow 3Ca(OH)_2(aq)+2PH_3(g)$
Add a coefficient of 6 to $H_2O$ to balance $H$ and $O$.
$Ca_3P_2(s)+6H_2O(l)\rightarrow 3Ca(OH)_2(aq)+2PH_3(g)$
