ok, thanks for that one
now i have another one, which is due in soon

The postcode on an envelope is a four-digit number. The sum of the digits is even. The first two digits form a two-digit number divisible by 9. The first and third form the square of a whole number, and the second and fourth form a multiple of 11. What is the postcode?
So far I have this:

Let x = the post code
So x = abcd
So a+b+c+d / 2 = 0
And ab / 9 = 0
Possibilities for ab
9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99

And ac could be one of 1(1), 4(2), 9(3), 16(4), 25(5), 36(6), 49(7), 64(8) and 81(9)

And bd / 11 = 0
Possibilities for ac
11, 22, 33, 44, 55, 66, 77, 88, 99

There must be an even amount of the same type of digits.
For Example:
if
a is odd
b is even
c is odd
then
d has to be even

OK?

Thanks