Show that a f: Z -> R , n -> n*1(subr) is a homomorphism of rings

Homework Statement

Show that a f: Z → R , n → n*1R is a homomorphism of rings

The Attempt at a Solution

f(a+b) = f(a) + f(b)
f(a*b) = f(a) * f(b)
f(1Z) = 1R

Ok, so if I actually have a clue what the problem statement means -- which is just slightly possible -- then this function maps values 'n' to 'n' times the identity unit of R. Which is equal to the identity unit of Z, so I think that part of the definition is more-or-less covered.

How do I go about using the first two parts of the definition?

The function is just f(n) = n right?
so do I just sub in (a+b) for n?
f(a+b) = f(a) + f(b) ???
Is there anyway I can actually show that this is the case? I mean isn't this intuitive/properly defined upon the integers?

same for the other part
f(ab) = f(a)*f(b) ..... i'm just not sure how to actually show this...

thanks for any help.