Answer
$CH_3OCH_3(g)+3O_2(g)\rightarrow 2CO_2+3H_2O$
Work Step by Step
The basic reaction is:
$CH_3OCH_3(g)+O_2(g)\rightarrow CO_2+H_2O$
Add a coefficient of 3 to $H_2O$ to balance $H$.
Add a coefficient of 2 to $CO_2$ to balance $C$.
$CH_3OCH_3(g)+O_2(g)\rightarrow 2CO_2+3H_2O$
Add a coefficient of 3 to $O_2$ to balance $O$.
$CH_3OCH_3(g)+3O_2(g)\rightarrow 2CO_2+3H_2O$
