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.