Okay, so keeping mind that the equation for area is A = L x W, look at the measurements you already have. 5.5 x 10^5 is the length, and 4.2 x 10^4 is the width. Switch them into full form and use a calculator to multiply the two for the area in meters.
550000 x 42000 = 23100000000, which in scientific form is 2.31 × 10^10. So that's answer one.
For the second, in kilometers, just take the full measurement you already have, 23100000000 m, transfer it into kilometers, 23100000 km, and then find its scientific notation, 2.31 × 10^7. That's answer two.
To answer the last question for which is more suitable, just consider what number you'd prefer to look at: a bigger number or a smaller one. Since the kilometer measurement number is smaller, its correct.
Summarily, the answers are 2.31 × 10^10, 2.31 × 10^7, and square kilometers, in that order.
