To solve the equation \( 21x + 1,998 = 2,243 \), we'll first isolate \( x \).
- Subtract \( 1,998 \) from both sides:
\[ 21x = 2,243 - 1,998 \]
- Calculate the right side:
\[ 2,243 - 1,998 = 245 \]
So now we have:
\[ 21x = 245 \]
- Divide both sides by \( 21 \):
\[ x = \frac{245}{21} \]
- Perform the division:
\[ x \approx 11.67 \]
Now, given the choices (1, 10, 100, 1,000), the best estimate for \( x \) is \( 10 \), as it is the closest to \( 11.67 \).
Thus, the best estimate for \( x \) is:
10