UPD: Here’s the solution for just the additions and multiplications:
The formula is:
thisRow.Expression.RegexReplace("\s", "").Split("+").FormulaMap(
CurrentValue.Split("*").FormulaMap(CurrentValue.ToNumber()).Product()
).Sum()
where RegexReplace("\s", "") removes spaces within the expression, then we split it by additions to get numbers and sequences of multiplications, then for each of those pieces we split by multiplication sign and find a product, and finally sum all those together.