docs(optional-sum): correct grammar

subjects/mobile-dev/optional-sum/README.md

@@ -1,32 +1,30 @@
-# Optional Sum
+## Optional Sum
 
 ### Instructions
 
-Write a function called `optionalSum()` that accepts two integer arguments, and an optional integer argument. Return the sum of all the arguments.
+Write a function named `optionalSum` that accepts two `int` arguments, and an optional `int` argument. Return the sum of all the arguments.
 
 ### Optional parameters
 
-In Dart you can also make function arguments optional, meaning that a function can work even if the optional argument is omitted. If the optional parameter is omitted, it is considered to be null.
+In Dart, you can make function arguments optional, meaning that a function can work even if the optional argument is omitted. If the optional parameter is omitted, it is considered to be `null`.
 
-### Usage
-
-Example of function with optional parameters:
+A function with optional parameters:
 
 ```dart
-void someFunction(int firstParameter, int secondParameter, [int? optionalParameter]) {
-	if (optionalParameter != null) {
-		print('${firstParameter}, ${secondParameter}, ${optionalParameter}');
+void someFunction(int first, int second, [int? third]) {
+	if (third != null) {
+		print('${first}, ${second}, ${third}');
 	} else {
-		print('${firstParameter}, ${secondParameter}');
+		print('${first}, ${second}');
 	}
 }
-void main() {
 
+void main() {
 	someFunction(1, 2);
 	someFunction(1, 2, 3);
 }
 ```
 
-- Note: Optional parameters must come after the required parameters.
+> Optional parameters must come after the required parameters.
 
-- Note: You cannot use both optional and named parameters, you should choose only one of them.
+> You cannot use both optional and named parameters.