If you have an excel worksheet with a list of the unit weights against the Section code then you can use Vlookup function to insert the unit weights.
See the following link for more information on Vlookup formula
Your table for the lookup should be something like the following. It can be on a separate worksheet.
Your vlookup formula will be like the following for cell E2 of your screen shot. Note that the lookup table is on a different worksheet and also note that the Table Array for the lookup is in absolute format (with the $ signs)
=VLOOKUP(A2,Sheet2!$A$2:$B$9,2,FALSE)
I also note that you have a different value in cell E15 that does not match the same section descriptions on the previous rows.
I would also suggest that you use list type data validation and for your column A and use the same list in column A as your list of Sections and Unit weights and that way you should never have a mismatch due to typos.
Feel free to get back to me if still having problems.