>I am looking for a formula that can give me the amount of sale before tax.
>
>I have a amount and I know the rate of Canadians taxes ( GST and PST) and I like to found out was the amount before taxes for the GST and PST.
>
>Any one did this before?

Yes, I do it all the time. However, keep in mind that it may vary by 1 cent as you can't know if rounding was applicable.

Assuming This.Value is your value:

ThisForm.Cout.Value=ROUND(This.Value/1.15025,2)
ThisForm.Tps.Value=ROUND(ROUND(This.Value/1.15025,2)*.07,2)
ThisForm.Tvq.Value=This.Value-(round(This.Value/1.075,2))