Explanation

Complementary angles are a pair that add to 90°, so the complement of 80° is 90° − 80° = 10°. The degree-to-radian conversion uses the relation 180° = π radians, so 10° = 10 × (π/180) = π/18 radians. Hence option (c). The distractors mix up the conversion factor: 5π/9 radians equals 100° (a mis-computed complement), while 18/π and 9/(5π) come from inverting the π/180 multiplier.