The mass of jupiter is 1.898 × 10(27) kilograms, and the mass of saturn is 5.68 × 10(26) kilograms. how much greater is jupiter's mass than saturn's mass?

Just subtract but take care of the power or else you can come up with wrong results !

so first make the power same ;

for Jupiter = 1.898× 10(27) = 18.98 × 10(26)
for Saturn = 5.68×10(26)

so now subtract = (18.98-5.68) × 10(26)
= 13.3 × 10(26)

so the answer is 13.3 ×10(26)
or, 1.33× 10(27)