A two-digit number is such that the sum of its digits is 9. If 27 is added to the number, the digits get reversed. What is the number?

✓ Correct Answer: Option B

Let the number be 10t + u. (1) t + u = 9. (2) 10t + u + 27 = 10u + t. Simplifying (2) gives 9t - 9u = -27, or t - u = -3. Solving t+u=9 and t-u=-3 yields t=3, u=6. The number is 36.