NULL (blank) problem

Hello everyone;
In the attached spreadsheet, Row-3 gets it values from Row-2 (it's a cumulative total). I need some assistance for a formula statement like this;

If F2, G2....is NULL, then F3,G3....is also NULL
If F2, G2...is a number (including 0), then continue with cumulative total.

Note that row-2 is manually entered. Row 3 relies on row-2 to continue with its total.

Can this be done? Will appreciate any help folks!

Thanks