The answer is √91 feet (which is the same as 9.54 feet).
Imagine this as a right triangle. A length of the foot is actually a hypotenuse (c). The distance from wall's base to the ladder foot is one of the sides of the triangle (let it be a). So, using the Pythagorean theorem: c² = a² + b² It is given: c = 10 feet a = 3 feet b = ? c² = a² + b² ⇒ 10² = 3² + b² 100 = 9 + b² b² = 100 - 9 = 91 ⇒ b = √b² = √91 ≈ 9.54 feet
