a) Both rational and irrational numbers. The radical symbol 25 and radical symbol 9 are rational numbers (5 and 3, respectively), while the radical symbol 64 is an irrational number (8).
b) Both rational and irrational numbers. -2.4 and 3.1 are rational numbers, 0 is a rational number, and the radical symbol 81 is a rational number (9).
c) Both rational and irrational numbers. -2/3 and 7/9 are rational numbers, while π/2 is an irrational number.
d) Both rational and irrational numbers. The radical symbol 12 is an irrational number (approximately 3.464), the radical symbol 11 is also an irrational number (approximately 3.317), and π is an irrational number.