Answer:
s = 19.0
Step-by-step explanation:
To find s, use the Pythagorean Theorem.
a² + b² = c²
9² + b² = 21²
81 + b² = 441
b² = 360
b = √360
b = 18.97366596 ⇒ 19.0 (rounded to the nearest tenth)
So, s = 19.0.
Hope that helps.
