If six inch clapboard siding is 72 cents per lineal ft and you need to cover 400 square ft so how do you figure the cost for the job?

2x 6" (x1ft) lengths = 1sq ft, so 2x 400 = 800 lineal feet is required.

800ft x 72 cents = $572

+10% for offcuts etc

Hope this helps,

Andy