Intro Physics question

I'm not quite sure where to start with this.

Thank you in advance

 

Well my professor hasn't given any examples yet on this and I can't find any in my textbook either. I was hoping someone could give me pointers on where to start.

 

I haven't done any physics or math in over a year which is probably why I'm having trouble with pretty basic problems.

Here's my attempt:

(a) Area of slick = [itex]\pi[/itex]r²
diameter of slick = 2x10¹⁰
volume of slick= area x thickness
volume of oil=volume of slick= 1L = 0.001m³

0.001m³=([itex]\pi[/itex]r²
r=1261.57m
d=2523m


(b) [itex]\rho[/itex]=M/V
V=[itex]\pi[/itex]r³
=[itex]\pi[/itex](1x10^-10)³
V=3.14x10^-30m³
M=850kg/m³ x 3.14x10^-30m³

M=2.67x10^-27kg

does that make sense?

 

Thank you!

The diamete/thickness was a typo, I wrote it properly on my sheet :)

As for the significant digits, does 2.5x10³m work?