Answer
$CaC_2(s)+2H_2O(l)\rightarrow Ca(OH)_2(aq)+C_2H_2(g)$
Work Step by Step
$CaC_2(s)+H_2O(l)\rightarrow Ca(OH)_2(aq)+C_2H_2(g)$
Add a coefficient of 2 to $H_2O$ to balance $H$ and $O$.
$CaC_2(s)+2H_2O(l)\rightarrow Ca(OH)_2(aq)+C_2H_2(g)$