## Plain Sum

### Instructions

Create a function named `plainSum`, which accepts 3 `int` parameters, and returns their sum.

Functions in Dart are declared like this:

```dart
bool isEven(int num) {
  return num % 2;
}
```

### Usage

```dart
void main() {
  var result = plainSum(1, 2, 3);
  print(result); // prints 6
}
```