For this you are going to move the decimal point to the left.
So 2910000. You are going to count how many times you move the decimal to the left. You will stop once you once the decimal point is next to the first number. So it will look like this 2.910000 At this point you should have counted six spaces. So you can now put it in the correct form 2.91 x \(10^{6.}\)
Same with 140000. 1.40000 The decimal point moved five spaces.
1.4 x \(10^{5}\)