Use dimensional analysis to set up your problem. That way you simply cannot set it up incorrectly.
You have a measurement in feet, and you need an answer in inches. You are also armed with a conversion ratio relating feet to inches.
To end up with inches you must take your feet, divide by feet and multiply by inches, so
26 ft (1in/2ft) = x inches
13 inches = x inches.
Look at the units. Let them tell you how to set up the problem.
