the 7 8 9 - on the numberpad of my wired apple keyboard stopped working. Is there a fix for this problem?

Unfortunately the newer Apple keyboards are not fixable. Your best bet, is to take the keyboard to the local Apple Store or AASP and see if it is eligible for replacement under the warranty.

den.thed wrote:

Unfortunately the newer Apple keyboards are not fixable.

FWIW, a wired Apple keyboard isn't exactly new.