Standard form just means you have to write the number using digits (the standard form of three is 3). When a number is written out in words and contains the word "and" it's describing a decimal place. So, the answer is 38.97 kg
formula for area of a circle is pi * radius squared. Since the diameter is 8 you divide that by 2 to get 4 and you square it so it becomes 16. Then you multiply it by pi or 3.14 to get 50.24 and then you round.