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# Help - Error with Frog/Loop Challenge code

I am getting the following error and I can't figure out why: FrogStats.cs(21,17): error CS0019: Operator `+=' cannot be applied to operands of type`double' and `Treehouse.CodeChallenges.Frog' Compilation failed: 1 error(s), 0 warnings

Code:

namespace Treehouse.CodeChallenges { class FrogStats { private readonly Frog _tongueLength;

```    public FrogStats(Frog tongueLength)
{
_tongueLength = tongueLength;
}

public static double GetAverageTongueLength(Frog[] frogs)
{
double sum = 0;
double tally = 0;
double average = 0;

for(int i = 0; i < frogs.Length; i++)
{
Frog frog = frogs[i];
sum += frog;

i++;
}

average = sum / frogs.Length - 1;
return average;
}
}
```

}

FrogStats.cs
```namespace Treehouse.CodeChallenges
{
class FrogStats
{

public FrogStats(Frog tongueLength)
{
_tongueLength = tongueLength;
}

public static double GetAverageTongueLength(Frog[] frogs)
{
double sum = 0;
double tally = 0;
double average = 0;

for(int i = 0; i < frogs.Length; i++)
{
Frog frog = frogs[i];
sum += frog;

i++;
}

average = sum / frogs.Length-1;
return average;
}
}
}
```
Frog.cs
```namespace Treehouse.CodeChallenges
{
public class Frog
{
public int TongueLength { get; }

public Frog(int tongueLength)
{
TongueLength = tongueLength;
}
}
}
``` 