The solution presented in The Mathematics Teacher is shown below.

Focus on the above presentation a minute and you will become aware of the large cognitive load involved.

The method of handling units is compact and can be used by those well versed in the subject matter involved. For those learning a subject the method can be quite difficult.

The following solution contains all of the steps that were done in constructing the above presentation. Anyone can see and follow this. Most important is the explicit focus on concepts.

The important feature of the above solution is that it uses mathematics. Use of mathematics as a language is essential to developing thinking skills. Problem solving is widely presented in a "scheme" oriented framework. A process that focuses on using mathematics as the basic tool for solving word problems has advantages that go well beyond simply getting the answer to the problem at hand.