Answer:
b = 20
Step-by-step explanation:
The triangle is a right triangle, so the Pythagorean theorem applies.
a² + b² = c²
21² + b² = 29² . . . . . . . . . fill in the given values
b² = 841 -441 = 400 . . . . subtract 21²
b = √400 = 20 . . . . . . . . take the square root
Side b is 20 units long.
