Two parallel chords are drawn in a circle of radius 15 cm. The length of one chord is 24 cm and the distance between two chords is 21 cm. The length of the other chord is-

For first chord (24 cm) in circle of radius 15 cm: half chord = 12 cm. Distance from center d₁ = √(15² - 12²) = √(225-144) = √81 = 9 cm. Distance between chords is 21 cm, so d₂ = |21 ± 9| = 12 cm or 30 cm. Since 30 > 15, d₂ = 12 cm. Half of other chord = √(15² - 12²) = √(225-144) = 9 cm. Full chord = 2 × 9 = 18 cm. Option A is correct.