What is the fewest number of steps (changing one letter at a time, with each step yielding a common English word) in which you can change "HOT" into "AIR" and then "AIR" into "BAG"?
H O T
. . .
. . .
A I R
. . .
. . .
B A G
HOT -> HIT ->SIT -> SIR -> AIR -> FIR -> FIG ->BIG ->
BAG