sumproduct?

[plasteredric]

Im trying to do the following if anyone can help.
Formula cell is A10

=SUM(B7/Sum(B3,B4,B5))
Example: Sum ( 10 / Sum ( 1, 1, 3)) = 2

Now the hard part, i need to complete the above for columns B to G all in the same formula, the only way I can think of doing it is to have an extra row which does the Sum(B3,B4,B5) part.

Columns B to G are the same format, values will change but for the above example they can all be the same.
The expected result from the formula would be 12.

Any suggestions appreciated.

Thanks