Task
📝 **Task:** Mini-calculator `calc(a, op, b)`. Support `+`, `-`, `*`, `/`. Division by 0 → `"Error"`.
📋 **Steps:**
1. `def calc(a, op, b):`
2. Check `op` via `if`:
- `"+"` → `return a + b`
- `"-"` → `return a - b`
- `"*"` → `return a * b`
- `"/"` → if `b == 0` return `"Error"`, else `a / b`
💡 **Similar example:**
```python
def simple_op(a, op, b):
if op == "+": return a + b
if op == "-": return a - b
return "Unknown"
```
🎯 **Expected output:** `15\nError`