SaverAccount“不实现接口成员”

Question

我是初学者，按照教册上的代码写的，但是调试的时候说SaverAccount不能实现接口成员，怎么一回事啊 ，望各位高手指点一下。谢谢 
下面是代码部分：
using Wrox.ProCSharp;
using Wrox.ProCSharp.VenusBank;namespace Wrox.ProCSharp
{
    class MainEntryPoint
    {
        static void Main(string[] arges)
        {
            IBankAccount venusAccount = new SaverAccount();
            venusAccount.PayIn(200);
            venusAccount.Withdraw(100);
            Console.WriteLine(venusAccount.ToString());
        }
    }}
namespace Wrox.ProCSharp
{
    public interface IBankAccount
    {
        void PayIn(decimal amount);
        bool Withdraw(decimal amount);
        decimal Balnce
        {
            get;
        }
    }
}namespace Wrox.ProCSharp.VenusBank
{
    public class SaverAccount : IBankAccount
    {
        private decimal balance;
        public void PayIn(decimal amount)
        {
            balance += amount;
        }
        public bool Withdraw(decimal amount)
        {
            if (balance >= amount)
            {
                balance -= amount;
                return true;
            }
            Console.WriteLine("Withdrawal attempt failed");
            return false;
        }
        public decimal Balance
        {
            get
            {
                return balance;
            }
        }
        public override string ToString()
        {
            return String.Format("Venus bank saver:Balance={0,6,C}", balance);
        }
    }
}