// solves an equation using earth with correct unknowns
    public static Steps SolveEarth(string[] quantities)
    {
        ConvertUnitsInArray(quantities);

        //construct an array that tells us which ones are known
        if (quantities.Length != 5)
        {
            throw new System.ArgumentException("invalid set of quantites");
        }

        bool[] knowns = ConstructKnowns(quantities);

        Earth solution = new Earth(knowns, quantities);

        solution.DoAlgebra();

        return(solution.GetWork());
    }