How do you balance this equation H2SO4+NH4OH—>(NH4)2SO4+H2O?

The balanced equation is:
##H_2SO_(4(aq))+2NH_4OH_((aq))rarr(NH_4)_2SO_4(aq)+2H_2O_((l))##
Sulfuric acid is diprotic so is able to give up 2 H+ ions. ##NH_4OH## is not a compound that can actually exist as a discrete substance. It is better described as ammonia solution which is formed from dissolving ammonia gas in water:
##NH_(3(g))+ H_2O_((l))rightleftharpoonsNH_(4(aq))^(+)+OH_((aq))^-##