Added task 3

basic programming/3rd task/7.py

@@ -0,0 +1,20 @@
+def duplicates_remove(txt: str) -> str:
+    seen = ""
+    result = ""
+    for char in txt:
+        if char not in seen:
+            result += char
+            seen += char
+    return result
+
+def main_7ex():
+    txt1 = "banana"
+    print(f'{txt1} {duplicates_remove(txt1)}')
+
+    txt2 = "apple"
+    print(f'{txt2} {duplicates_remove(txt2)}')
+
+    txt3 = "pear"
+    print(f'{txt3} {duplicates_remove(txt3)}')
+
+main_7ex()