So how could i round the outcome of a sum and divide? Because i need a specific number but this number would never be the same.

I tried this:

```
$set: {
power: { $sum: ["$power", "$attack", "$defence", { $divide: ["$endurance", 3] }, { $round: [$sum, 2] }] }
}
```

And this:

```
$set: {
power: { $sum: ["$power", "$attack", "$defence", { $divide: ["$endurance", 3] }, { $round: [power, 2] }] }
}
```

But both turn up:

ReferenceError: power is not defined

ReferenceError: $sum is not defined

Right now the output is: 9.333333333333334, but i would like 9.3.