Dlookup in form

Hi

I am looking to get the value selected from a combo-box to select a value from a field in a table.

Fields in Lookup table: Prefix (A), Description (A), base number (N)

when Prefix is selected in combo box I want to return the number in base number.

Also will the number auto update in lookup for that record?

Can anyone help?

Thank you

Dlookup in form