diff --git a/3exercises/ex20.py b/3exercises/ex20.py
new file mode 100644
index 0000000..2dd61b9
--- /dev/null
+++ b/3exercises/ex20.py
@@ -0,0 +1,33 @@
+from sys import argv
+
+script, input_file = argv
+
+def print_all(f):
+    print(f.read())
+
+def rewind(f):
+    f.seek(0)
+
+def print_a_line(line_count, f):
+    print(line_count, f.readline())
+
+current_file = open(input_file)
+
+print("First let's print the whole file:\n")
+
+print_all(current_file)
+
+print("Now let's rewind, kind of like a tape.")
+
+rewind(current_file)
+
+print("Let's print three lines:")
+
+current_line = 1
+print_a_line(current_line, current_file)
+
+current_line = current_line + 1
+print_a_line(current_line, current_file)
+
+current_line = current_line + 1
+print_a_line(current_line, current_file)
diff --git a/Codecadmey Projects/ex7_ch3,L1?.py b/Codecadmey Projects/ex7_ch3,L1_.py
similarity index 100%
rename from Codecadmey Projects/ex7_ch3,L1?.py
rename to Codecadmey Projects/ex7_ch3,L1_.py
diff --git a/PHW.md b/PHW.md
index 3ab16e6..7d626ad 100644
--- a/PHW.md
+++ b/PHW.md
@@ -1,3 +1,15 @@
-#
+# Function Checklist (ex19)
 
-ex19.
+1. Did you start your function definition with def?
+2. Does your function name have only characters and _ (underscore) characters?
+3. Did you put an open parenthesis right after the function name?
+4. Did you put your arguments after the parenthesis separated by commas?
+5. Did you make each argument unique (meaning no duplicated names)?
+6. Did you put a close parenthesis and a colon after the arguments?
+7. Did you indent all lines of code you want in the function four spaces? No more, no less.
+8. Did you “end” your function by going back to writing with no indent (dedenting, we call it)?
+When you run (“use” or “call”) a function, check these things:
+1. Did you call/use/run this function by typing its name?
+2. Did you put the ( character after the name to run it?
+3. Did you put the values you want into the parentheses separated by commas?
+4. Did you end the function call with a ) character?