The area \( A \) of a rectangle can be calculated using the formula:
\[ A = \text{length} \times \text{width} \]
To solve for the width, we can rewrite the formula as follows:
\[ \text{width} = \frac{A}{\text{length}} \]
Now, we can use this rewritten formula to find the width of a rectangle with an area of \( 42 \) square inches and a length of \( 16.8 \) inches.
Substituting the values into the formula:
\[ \text{width} = \frac{42}{16.8} \]
Now, we perform the division:
\[ \text{width} = 2.5 \]
Thus, the width of the rectangle is \( 2.5 \) inches.