I need help with 3 and 4 :)

Can someone explain to me how to do

One astronomical unit (1 au) is about 1.496 alt tag missing. kilometers. if you wrote this number of kilometers in regular decimal notation (for example, 528 and 3,459 are written in regular decimal notation), how many zeros would your number have?

If a and −a are numbers on the number line, which expression must give the distance between them? a) 0 b) a c) |2a| d) |a|