Trying to understand this. Problem states "The radius of a circular disk is given as 24cm with a maximum error of 0.2cm. An estimate, via linearisation, of the maximum error in the calculated area of the disk is ?

This is what I have done and think it's right.

The answer is given as being

But I would have thought it to be

Am I completely out of my mind? What am I not getting here?(Headbang)