Puzzle ZCAG 

Workings

Hint
There are 12 inches in a foot, and 1,760 yards in a mile.

Answer
Feet in a 20-mile walk.

Reasoning
There are 12 inches in a foot, 3 feet in a yard, and 1,760 yards in a mile:

   square inches in a piece of carpet 15 yards by 5 yards
      (15 x 3 x 12) x (5 x 3 x 12) = 97,200 square inches.

   feet in a 20-mile walk
      20 x 1760 x 3 = 105,600 feet.