Assuming your data extends to 5 rows from row 1, try this single-cell formula:
{=SUM(IF(A1:A5="Potomac", B1:B5 + C1:C5, 0))}
This is an array formula, meaning you don't actually type the braces, but use Ctrl + Shift + Return once you've done editing.
(I'm at home without Excel so am doing this from memory. If it doesn't work it means I've slipped the syntax. Do let me know.)