Solve Addition Problem: 855 + 117 in Vertical Format

To solve this problem, we'll use vertical addition, a method of adding numbers by aligning them by their rightmost digits (unit place) and dealing with carrying as necessary:

• Step 1: Align the numbers by place value:
      $\phantom{+}855 \\$ + $\phantom{+}117$
• Step 2: Add the digits in the unit's place:
  The digits in the unit's place are $5$ and $7$. Adding them gives $12$. Write down $2$ in the unit column and carry over $1$ to the tens column.
• Step 3: Add the digits in the ten's place:
  The digits in the ten's place are $5$ and $1$, plus the carried over $1$, giving us $7$. Write $7$ in the tens column.
• Step 4: Add the digits in the hundred's place:
  The digits in the hundred's place are $8$ and $1$. Adding them gives $9$.

Summing these gives us the total:
    $\phantom{+}855 \\$ + $\phantom{+}117 \\$   \underline{\phantom{.}972} \)

Thus, the answer is $972$.