Suppress Formula Fields And Text Object In Crystal Reports

Question

I have a formula field on crystal reports. I wants to check it whether it may consists negative value or not if it has
negative value than suppress it or hide it.

My formula field name is "Bal"  which consists formula is as below:

WhilePrintingRecords;

Shared NumberVar mytot;

mytot:={@TotalSale}-{@TRPurchaseTotal}

How to suppress Formula field and TextObject?.