Step-by-step Solution:

\[ \textbf{Step 1: Let the original number be } x. \] \[ \textbf{Step 2: After increasing by 15%, the number becomes: } x + 0.15x = 1.15x. \] \[ \textbf{Step 3: Given that } 1.15x = 161. \] \[ \textbf{Step 4: Solve for } x: \quad x = \frac{161}{1.15}. \] \[ x = 140. \] \[ \textbf{Final Answer: } \boxed{140} \]