Sorry, you did not specify this was ASP, I thought it was PHP
in ASP
&& [VolumeDiscount] == 7
should be:
AND [VolumeDiscount] = 7
to have multiple break points, you need multiple conditions:
((Abs([Quantity]>=3 AND [Quantity]<=9 [VolumeDiscount] = 7)*[Price]*0.1) + ((Abs([Quantity]>=10 AND [Quantity]<=19 [VolumeDiscount] = 7)*[Price]*0.15) + ((Abs([Quantity]>=20 AND [VolumeDiscount] = 7)*[Price]*0.2)