Excel Formula help please

Question

Below is a copy of a spreadsheet I am working on.

I need column E to read zero until a figure is put into the quantity.

The current formula in E is =SUM(G7*SUM(D7/(1-$L$4%))+E7) which when you put the figure in the quantity does calculate correctly, but I just don't want a figure in the final column until requested by the quantity.

Hope that makes sense, probably really simple

Thanks

Supplier Cost	Sell Install Cost	QUANTITY	TOTAL COST	SELL
£40.42	£196.88		£0.00	£196.88
£145.84	£196.88		£0.00	£196.88
£137.09	£196.88		£0.00	£196.88
£132.09	£196.88		£0.00	£196.88

Supplier Cost	Sell Install Cost	QUANTITY	TOTAL COST	SELL
£40.42	£196.88	1	£237.30	£297.93
£145.84	£196.88	1	£342.72	£561.48
£137.09	£196.88	1	£333.97	£539.61
£132.09	£196.88	1	£328.97	£527.11

Answer 1

Thank you

That worked perfectly

Answer 2

Amend Hans' formula to:

=IF(G7="",0,G7*D7/(1-$L$4%)+E7)

Answer 3

Thanks you.

Sorry for being so confusing

so lets rename the columns to

D, E, G, H, I

The reference to column L in the formula relates to a changeable figure

D	E	G	H	I
Supplier Cost	Sell Install Cost	QUANTITY	TOTAL COST	SELL
£40.42	£196.88		£0.00	£196.88
£145.84	£196.88		£0.00	£196.88
£137.09	£196.88		£0.00	£196.88
£132.09	£196.88		£0.00	£196.88

Answer 4

You don't need SUM. The formula can be simplified to

=G7*D7/(1-$L$4%)+E7

But a formula in E7 cannot refer to E7 itself, so I don't understand what you're doing.