I think my Apple IIc has faulty RAM chips and I would like to exchange them.

Which RAM chips should I use?

In particular, which is the right speed?

I checked my Apple IIc RAM chips and in the middle there is Apple logo followed by "mT 4264".

On the top of the chips is written, with a very little font, "8448".

There are no values such -20, -15, -1,2 -10, -8 to know their speed.