Answer & Explanation:
The formula in the cell B7 would be:
"=B5-B6"
And now we will press "Ctrl+C" to copy the formula in the Cell B7. After copying we will select the cell range C7 to D7 and press "Ctrl+V" to paste this formula in the cell C7:D7 and then will press Enter key. Now what we see is results in C7:D7 which we can check in our calculator whether these are corectly calculated or not.
If you have glasses the liquid and cloth can be used to clean it. You spray the camera, then use the cloth to wipe it up. If you don't have them the dollar store should have some, or even places like Walmart and Maceys.