Make the following changes to the number 7.849: make the 7 worth 1/10 as much.

So you want 7 to be 1/10 of much. Pretty easy. All you need to do is change 1/10 into a decimal by dividing.

1 : 10 = 0.1

Now you multiply 7 and 0.1

7 * 0.1 = 0.7

So your answer is 0.7!