The difference between the masses is
4.55·10¹³ kg -1.78·10¹² kg
= 4.55·10¹³ kg - 0.178·10¹³ kg
= (4.55 -0.178)·10¹³ kg
= 4.372·10¹³ kg
Rounded to the appropriate precision, the mass of the Antarctic iceberg exceeds that of the Rock of Gibraltar by ...
4.37·10¹³ kg