vc#3015 : Dbl3D class error

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace VR3D
{
    class Dbl3D
    {
        public double x;
        public double y;
        public double z;
        public Dbl3D(double a = 0.0, double b = 0.0, double c = 0.0)
        {
            x = a;
            y = b;
            z = c;
        }
        public Dbl3D operator +(Dbl3D a, Dbl3D b)
        {
            return new Dbl3D(a.x + b.x, a.y + b.y, a.z + b.z);
        }
        public Dbl3D operator -(Dbl3D a, Dbl3D b)
        {
            return new Dbl3D(a.x - b.x, a.y - b.y, a.z - b.z);
        }
        public Dbl3D operator *(Dbl3D a, double b)
        {
            return new Dbl3D(a.x * b, a.y * b + b, a.z * b);
        }
        public Dbl3D operator /(Dbl3D a, double b)
        {
            return new Dbl3D(a.x / b, a.y / b, a.z / b);
        }
         public static double lenght( Dbl3D v)
        {
            return Math.Sqrt(v.x * v.x + v.y *v.y + v.z * v.z);
        }
        public static double dot( Dbl3D a,Dbl3D v)
        {
            return a.x * v.x + a.y * v.y + a.z * v.z;
        }
        public static double angle(Dbl3D a, Dbl3D v)
        {
            double d, lt, lv;
            d = dot(a,v);
            lt = lenght(a);
            lv = lenght(v);
            return Math.Acos(d / (lt * lv));
        }
        public static Dbl3D cross(Dbl3D a,  Dbl3D v)
        {
            return new Dbl3D(a.y * v.z -a.z * v.y
                , a.z * v.x - a.x * v.z, a.x * v.y -a.y * v.x); 
        }
        public string toStr();
        {
            return "( ";x;" , ";y;" , ";z;" )" ;
        }
    };
}