You could sit down with several pencils and a whole pad of paper, and
divide Leda's mass by Europa's mass. But it's probably good enough
to provide an answer that's correct to 2 or 3 significant figures, and
there's a much easier way to do that:
Leda's mass . . . . approx. 1.094 x 10¹⁶
Europa's mass . . . . approx. 4.8 x 10²²
Leda's mass is about (1.094 x 10¹⁶) / (4.8 x 10²²) of Europa's mass.
(1.094 x 10¹⁶) / (4.8 x 10²²) = 2.28 x 10⁻⁷
Leda's mass is approx. 0.000 000 228 of Europa's mass.
