Calculate Side Length: Finding Square Root of Area 16

We need to determine the side length of a square whose area is 16.

• Step 1: Set up the equation using the area formula for a square, $A = s^2$. Given the area $A = 16$, we have:
  $s^2 = 16$
• Step 2: Solve for $s$ by taking the square root of both sides:
  $s = \sqrt{16}$
• Step 3: Calculate the square root:
  $s = 4$

Since a side length cannot be negative, we take only the positive square root. Therefore, the side length of the square is $4$, which corresponds to choice 4.