If you've got rows of formulas that are similar (x+y=z), here's an easy way to have Excel solve those for you.
- Click the cell which contains the formula you want to copy.
- Click on the small black square in the lower-right corner of that cell, and hold the mouse button down.
- Drag the box down to cover all the cells you want to contain that formula.
- When you let go of the mouse button, you will see those cells populate with the formula.