To find the thickness of a fingernail, you need to add the thickness of the hair to the additional thickness given.
The diameter of a human hair is about \( 4 \times 10^{-3} \) inches, which is equal to 0.004 inches.
The thickness of a fingernail is about \( 0.011 \) inches thicker than the hair. Therefore, we add the two values together:
\[ \text{Thickness of fingernail} = 0.004 , \text{inches} + 0.011 , \text{inches} = 0.015 , \text{inches} \]
Now, rounding to three decimal places:
\[ \text{Thickness of fingernail} = 0.015 \]
Thus, the thickness of a fingernail is \( \text{0.015} \) inches.