Data Sufficiency

Can someone help me out with this DS question ?
It's from a test on Manhattan GMAT.

If (243)^x(463)^y = n, where x and y are positive integers, what is the units digit of n?

(1) x + y = 7

(2) x = 4

Will post the answer after a couple of replies. I didn't understand the explanation.

-B

If (243)^x(463)^y = n, where x and y are positive integers, what is the units digit of n?
(1) x + y = 7

(2) x = 4

Given:
(243)^x (463)^y = n;
Unit Digit of n = unit digit of ( (243)^x ) X Unit Digit of ((463)^y)
= 3^x * 3^y

1. x+y = 7 and ==>x ,y = {1,2,3,4,5.6}
= 3^(x+y)
=3^7
Unit Digit of n =1

Sufficient
Answer: A,D
2.x=4 ,no information on y .not sufficient
y={1...n}
if y=1 Unit digit is = 3^5
y=2 Unit digit is =3^6
Answer: A

Small Correction=:

=3^7
Unit Digit of n =1 ==> Unit Digit of n =7

thanks. A was the answer.
would you have a pointer to all these number/digit problem related formulae ?

thnx,
-B