1.

```rust
fn main() {
    let v = {
        let mut x = 1;
        x += 2
    };
 
    assert_eq!(v, ());
 }
```

```rust
fn main() {
    let v = {
        let mut x = 1;
        x += 2;
        x
    };

    assert_eq!(v, 3);
}
```

2.

```rust
fn main() {
    let v = {
        let x = 3;
        x
    };
 
    assert!(v == 3);
}
```

3.

```rust
fn main() {
    let s = sum(1 , 2);
    assert_eq!(s, 3);
}

fn sum(x: i32, y: i32) -> i32 {
    x + y
}
```