Given an array of numbers, use Python to find the sum of all the numbers
To find the sum of all the numbers in the given array 'arr', you can use Python's built-in `sum` function, like this:

```python
arr = [3, 6, 9, 12]
total = sum(arr)
print(total)
```
This will output `30`, which is the sum of all the numbers in the array `arr`.
arr = [3, 6, 9, 12]
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:
Given an array of numbers, use Python to find the sum of all the numbers

### Input:
arr = [3, 6, 9, 12]

### Response:
To find the sum of all the numbers in the given array 'arr', you can use Python's built-in `sum` function, like this:

```python
arr = [3, 6, 9, 12]
total = sum(arr)
print(total)
```
This will output `30`, which is the sum of all the numbers in the array `arr`.