Answer:
 13.6 feet  from the wall
Step-by-step explanation:
This is a Pythagorean theorem question
The ladder is the hypotenuse or c
the distance from the wall is a leg or a
and the wall is the other leg or b
a² + b² = c²
a² + 21² = 25²
a² + 441 = 625
   -441   -441
     a² = 184
     √     √
     √a² = √184
      b = 13.6