Describing RE's in English Language

Question

I have the following question from a past exam paper:

I am struggling to formalise their definitions within the necessary 15 word limit. So far I have:

i) The empty string or set of strings that contain zero or many a's OR b's OR both

ii) The set of strings that start with one or many a's, unless preceded by b's, followed by one or many a's with zero or many possible preceding b's.

My definitions seem rather cumbersome...I just don;t want to lose any info by oversimplifying the definition.