Consistent instructions and examples

I started off with "hints" that required the poor student to piece
together the information from incomplete bits. A complete example is
like a picture that is worth 1000 words and far clearer.

19_functions2.zig

@@ -1,5 +1,11 @@
 //
-// Now let's use a function that takes a parameter.
+// Now let's create a function that takes a parameter. Here's an
+// example that takes two parameters. As you can see, parameters
+// are declared just like an other types ("name": "type"):
+//
+//     fn myFunction( number: u8, is_lucky: bool ) {
+//         ...
+//     }
 //
 const std = @import( "std" );
 
@@ -13,16 +19,13 @@ pub fn main() void {
 }
 
 //
-// Oops! We seem to have forgotten something here. Function
-// parameters look like this:
-//
-//   fn myFunction( number: u8, is_lucky: bool ) {
-//       ...
-//   }
-//
-// As you can see, we declare the type of the parameter, just
-// like we declare the types of variables, with a colon ":".
+// Please give this function the correct input parameter(s).
+// You'll need to figure out the parameter name and type that we're
+// expecting. The output type has already been specified for you.
 //
 fn twoToThe(???) u32 {
     return std.math.pow(u32, 2, my_number);
+    // std.math.pow(type, a, b) takes a numeric type and two numbers
+    // of that type and returns "a to the power of b" as that same
+    // numeric type.
 }