Update query Error

Hi

     I want to update my query in my fields.this is my customization form

     180 is there i want to add remaing fileds.through update

update [PAY_EPCD1] set U_PayFormula1=180 +' /{U_DaysMonth}*{U_PresentDays}'

where U_ComCode = 'INSC'

getting an error:Operand type clash: numeric is incompatible with ntext

I need like these through update.

180/{U_DaysMonth}*{U_PresentDays}

Regards

Vinoth