Added tutorial 30

Author: James Lockhart

README.md

@@ -32,6 +32,7 @@ The companion to the Youtube tutorials
 - [Learning Solidity : Tutorial 27 Getting started with browser development using Metamask](https://www.youtube.com/watch?v=eog2eYrPEu0)
 - [Learning Solidity : Tutorial 28 Address book on the blockchain powered by Angular](https://www.youtube.com/watch?v=bvxKICus3bw)
 - [Learning Solidity : Tutorial 29 What is WEI and how is Ether defined?](https://www.youtube.com/watch?v=yOfYNUQVjxk)
+- [Learning Solidity : Tutorial 30 Gas Explained](https://www.youtube.com/watch?v=sPrYkYk_Beo)
 ### Support
 
 - [Invalid implicit conversion of arrays from storage to memory and vice-versa](https://github.com/willitscale/learning-solidity/blob/master/support/INVALID_IMPLICIT_CONVERSION_OF_ARRAYS.MD)

tutorial-30/Gas.sol

@@ -0,0 +1,37 @@
+pragma solidity ^0.4.0;
+
+contract Gas {
+
+    string[] dataStore;
+
+    function cheap(uint a, uint b)
+        public
+        pure
+        returns (uint c)
+    {
+        c = a + b;
+    }
+
+    function expensive(string memory val)
+        public
+    {
+        dataStore.push(val);
+    }
+
+    function average()
+        public
+        view
+        returns (string memory)
+    {
+        return dataStore[0];
+    }
+
+    function low()
+        public
+        pure
+        returns (string memory)
+    {
+        string memory myString = "test";
+        return myString;
+    }
+}