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