Solve the Equation: Finding the Missing Value in 1800 + □ = 2100

To solve the problem $1800 + \Box = 2100$, we need to determine the value of $\Box$ that, when added to 1800, equals 2100.

We'll follow these steps:

• Step 1: Rearrange the equation to solve for the unknown $\Box$.
• Step 2: Perform the subtraction: $\Box = 2100 - 1800$.

Let's perform the calculation:

Step 1: Write the equation for $\Box$:

$\Box = 2100 - 1800$

Step 2: Calculate the difference:

$2100 - 1800 = 300$

Thus, the value of $\Box$ is $300$.

Therefore, the solution to the problem is $\Box = 300$.