Final answer:
The irrational numbers from the given list are only π (pi), since 4, -8.4, 0.898989..., and 9 can all be expressed as fractions or have a terminating/repeating decimal representation, making them rational numbers.
Step-by-step explanation:
The question about which numbers are not irrational can be answered by understanding the definition of irrational numbers. An irrational number cannot be expressed as a fraction or decimal that terminates or repeats. Given the list of numbers: 4, -8.4, π (pi), 0.898989..., and 9, we need to determine which are not irrational.
Number 4 is an integer, and thus it can be written as a fraction (4/1), making it a rational number. The number -8.4 is a negative decimal, but it has a finite number of digits after the decimal point, so it can also be expressed as a fraction (-84/10), meaning it is rational. The number π (pi) is a well-known irrational number because it cannot be exactly expressed as a fraction and its decimal representation goes on infinitely without repeating. The number 0.898989... repeats indefinitely, which implies it is a repeating decimal, therefore it's a rational number (it can be written as a fraction). Lastly, number 9 is a whole number and can be expressed as 9/1, hence it is rational.
The correct answer is that the numbers that are not irrational (i.e., are rational) are 4, -8.4, 0.898989..., and 9. Option 'c' from the original list is correct: '4, 9, -8.4, and 0.898989... only'.