Solve Vertical Addition: 81 Plus 9 Step-by-Step

The problem is to perform vertical addition for the numbers $81$ and $9$. Here’s the step-by-step approach:

• Step 1: Align the numbers vertically by their rightmost digits. The digit $1$ from $81$ is aligned with $9$.
• Step 2: Add the digits in the units place: $1 + 9 = 10$. Here, $10$ is a two-digit result, where $0$ remains in the units place and $1$ is carried to the tens place.
• Step 3: Add the digits in the tens place, including the carried digit: $8 + 1 = 9$. This accounts for the $1$ we carried over from the units place addition.

Since no further carrying is necessary, the result of adding $81$ and $9$ is $90$.

Therefore, the solution to the problem is $90$, which corresponds to choice 2.