1a. 64*10^6 +5.4*10^6 = 69.4*10^6 = 6.94*10^7 . . . . square miles
1b. 6.4*10^7 +0.54*10^7 = 6.94*10^7 . . . . square miles
.. yes, we can find the same answer this way
2. The ratio of areas is 6.4*10^7/(5.4*10^6) ≈ 11.85
The Pacific Ocean is about 12 times the size of the Arctic Ocean.
The difference of areas is 6.4*10^7 -0.54*10^7 = 5.86*10^7
The Pacific Ocean is 5.86*10^7 square miles larger than the Arctic Ocean.