Question 493189
Stack them up and do the addition or subtraction in the normal way. When you stack them stack them so the decimal points all line up on top of each other. Keep the decimal point in the same place in the answer as you had it in the stack.  In this case you are adding a negative, which is also known as subtraction. 
  5.4
- 9.7
-----
- 4.3

The trick here is to make SURE you stack your numbers by decimal place and move the decimal place directly down into the answer. ALWAYS have the decimal points lined up.