Well, it said "for a year."
Indeed. And this is exactly why performing simple arithmetic is a poor substitute for Algebra. You can tap out the solution for one year on your calculator, but then you have to keep running other scenarios through it in order to gain a half-useful understanding.
How much for the first year? *tap* *tap* *tap*
But we're planning on leaving in April... *tap* *tap* *tap*
Grr... I hate math.
What if we end up being delayed a couple months? *tap* *tap* *tap*
Or, you can just write out one expression, and instantly have a full conceptual understanding of how the two solutions relate. As I said, it's not the best question.
And of course, these problems are never this simple, because we haven't even looked at annual contracts, relocation costs, or equipment rent.
This scenario illustrates why so many people fail at family finances. You need Algebra to do it right.