Dee dee bought an apple for $0.85, a sandwich for $4.50, and a bottle of water for $1.50. how much did dee dee spend?

All you need to do is add these up. Get rid of the $ symbols, the fact that it's money doesn't play a part in the calculation. 

0.85 + 4.50 + 1.50 = 6.85

An easy way to make this easier is to add the part before the decimal place first so 4 + 1 = 5. Then add 0.5 + 0.5 that makes 1. So you have 6. Now you just have 0.85 left. So the answer is 6.85.

Add the cents that add the left overs to get the first number