add solutions for basic-types, fix errors

solutions/basic-types/statements.md

@@ -0,0 +1,47 @@
+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
+}
+```