please help me with these questions from abstract algebra.... Langrange theorem...

please help me with these questions from abstract algebra.... Langrange theorem...

Ans :−¿Let f :G → H be a homomorphism of groups∧define the kernel of f byker ( f )={ g ∈G| f ( g ) =e }Claim that ker ( f ) is subgroup for GSubgroup test :−¿Since G is group so...