First, make three forms: a purchase form, a sales form and the last balance form.

2. Make the header of the purchase table;

3. Make the header of the sales report;

4. Make the header of the balance table;

5. Open the balance table, put the mouse in cell b2, and then click FX in the bulletin board;

6. After confirmation, "Function Parameters" will pop up on the page. Click the up arrow at the end of the first line with the mouse. After clicking, the parameter function will become a separate line, and then click the purchase table;

7. After clicking the purchase form, the page will jump to the interface of the purchase form, and select the whole column where the "product name" is located; Click the up arrow behind "Parameter Function" after selection;

8. Click the blank space in the second line, the page will jump to the balance table, select cell B2, and click OK;

9. Click the up arrow in the third row, and then click the purchase list. The page will jump to the purchase list, select the whole column where the quantity is located (that is, column C), and click OK after selection;

10. After confirmation, the page will jump to the balance table, select cell b2, and place the mouse in the lower right corner of the cell. When the "+"sign appears in the cell, press and drop it down, which is enough to fill the formula of the second cell into other cells in column B;