@mengsheng
There is an Excel v4.0 macro function called "EVALUATE" which we can use to solve the equation you have in column G and H.
In the attached file, I created two Named Ranges like below...
Value_G =EVALUATE(Sheet1!$G2)
Value_H =EVALUATE(Sheet1!$H2)
Then I placed this formula...
In I2
=Value_G+Value_H

Remember to save the file as Excel Macro-Enabled Workbook since EVALUATE is a Macro Function.
Please refer to the attached for more details.