If value is blank, delete content in selected cell

I have a workbook where in column A I have a left statement =Left(B24,3) it gives me like 101, but if there is nothing it is blank, which is what I want. But then there is a macro which takes into account anything in column A and even though the cell is blank there is a formula in there. So, I was wondering if there is any formula that could change that so that the cell's contents would be cleared if there is no value in B24

Thanks!