Google Sheets Formula for Conditional Sum (drop down menu)

I need a Google Sheets expert to create a formula for me. It should sum values based on the selection from a drop-down list. The numerical value is in another column in the same row and needs to be totaled based upon the selection of the dropdown menu. You should have previous experience working with Google Sheets and be able to handle conditional sums.

Key requirements:
- Sum of values based on a text selection from a drop-down list.
- Handling conditional sums based on multiple conditions.
- Expertise in Google Sheets formulas.