2.3x10^19 kg
This is a matter of multiplication using scientific notation. First, multiply the mantissas
3.5 * 6.6 = 23.1
Then add the exponents
-2 + 20 = 18
So we initially have 23.1x10^18
But 23 is too large (the number has to be greater than or equal to 1 and less than 10). So divide the 23.1 by 10 and add 1 to the exponent, getting
2.31x10^19
Then since the least accurate value we have for input has only 2 significant digits, round the result to 2 significant digits, getting
2.3x10^19 kg
