complex if statement

[kdel1201]

column B contains a value of either "F" or "H" or blank
column C contains a value of either "A" or B" or blank
columns D-G contain various numeric values

In column A here is what I want to be returned:

if column B="F" return the value of 20; if column B="H" return the value of
10; if column B is blank, add together the values in columns D-G

AND

if column C="A" return the value of 20; if column C="B"= return the value of
10; if colum C is blank, add together the values in columns D-G (and column B)