A number is doubled and 9 is added. If the resultant is trebled, it becomes 75. What is the number?
Answer: B
Let the number be x. We work backward from the result.
Before being trebled, the number was 75 / 3 = 25.
This resultant (25) was obtained after doubling the number and adding 9. So, 2x + 9 = 25.
2x = 25 - 9 = 16.
x = 16 / 2 = 8.