You can obtain an explanation for any step by clicking on it.
So, you just need to click on line 14 and you will get the explanation.
If you are not satisfied with the number of solution steps displayed (either too many steps or too few), click on the Options button to adjust the number of steps to be shown. On the same screen, you can select integer or real arithmetics to be used during the solution process (e.g., x=1/2 vs. x=0.5). It is important to understand that if integer arithmetics is chosen, then all decimal numbers will be converted to integer fractions as part of the solution process.
This may produce a solution that is long and somewhat confusing.