In estimation questions don't be afraid to have a go with a guess
at some numbers in the problem and then to refine your estimate
after checking it makes some sort of sense.
Although there is no 'right' answer to an estimation, there are
good or bad estimations and sensible or over-detailed
calculations.
Think how you might make your estimation a good one, and think how
it makes sense to ignore certain complexities in the
calculation.
Use your skill and knowledge to place various scientific lengths in order of size. Can you judge the length of objects with sizes ranging from 1 Angstrom to 1 million km with no wrong attempts?