For the first part of your question it’s just a standard form question so split your question multiply 3.9 and 7.3 and add the indices together so it should look something like this
3.9 x 7.3 = 28.47
Then have your indices added because we’re multiplying so it should be
10 to the power of five so your answer should be 28.47 x 10 to the power of 5
