Final answer:
The solution set for the inequality 5x-9<21 is found by adding 9 to both sides and then dividing by 5, resulting in x < 6, which corresponds to answer D) x<6.
Step-by-step explanation:
The solution set of the inequality 5x-9<21 is found by isolating x. To solve for x, we would add 9 to both sides of the inequality, giving us 5x < 30. Then, by dividing both sides by 5, we will find that x < 6. This means the correct answer is D) x<6.