A cell can contain either a constant, static, value or a formula,
not both. If it contains a formula, you must write the formula to
return the desired result.
if it is always the same number within the formula that changes you could
have the number in a seperate cell and the formula would always calculate
with the newest number,ie instead of 4*3 in a1 which you change to 4*2 or
4*5,you could have =4*b1 in a1 and type your new number in b1.