RSA key requirements so that it can decrypt a DES key I came upon a solved exercise that uses a client's RSA key to encrypt a DES key. It has the following phrase:

value of n for RSA key generation has been chosen accordingly so that the DES key can be encrypted.

However it does not go on to explain what the requirements are and why. Could someone point this out to me? Many thanks.
A DES key is 56 bits long or 8 ASCII(7 bit) characters.
The rsa public key n must be larger than that.
However RSA key only barely big enough to hold a DES key would give almost no security at all.
Common RSA key lengths today are 2048 or even 4096 bits long.
512bit RSA keys which used to be reasonably common can now be broken in minutes with commercially available cloud services. So big enough to be even remotely secure will be much bigger than the minimal size to encrypt a DES key.
P.s
If you want to use OAEP (and you do) you need some extra wiggle room beyond the raw message size but still don't go anywhere near secure key length.