How to get the value of stored mathematic formula

Hi Nav masters,
My client want me to create a table that contain mathematic formula for their calculation. The idea is to store an mathematic formula ex: (A+B)*(A+C)
then store A,B,C in a different table as parameters.
I managed to create both table and insert the value of A,B,C into my formula
Ex: A=1, B=2, C=3
I managed to get String of (1+2)*(1+3)
My question is, how to get the value, because it is a string and i cant convert it into decimal
](*,) ](*,) ](*,)

Is there any other idea to store formula in table.
This is so that user can create many formula and the parameters is dynamic.

Thanks in advance