To find the thickness of a fingernail, we can add the thickness of the human hair to the additional thickness mentioned.
The thickness of a human hair is given as \( 4 \times 10^{-3} \) inches, which can be converted to decimal as follows:
\[ 4 \times 10^{-3} = 0.004 \text{ inches} \]
The additional thickness of a fingernail is given as \( 0.011 \) inches.
Now, we add these two values together:
\[ \text{Thickness of fingernail} = \text{Thickness of hair} + \text{Additional thickness} \] \[ \text{Thickness of fingernail} = 0.004 + 0.011 \] \[ \text{Thickness of fingernail} = 0.015 \text{ inches} \]
Rounded to three decimal places, the thickness of the fingernail is:
\[ \text{Thickness of fingernail} = 0.015 \]
So the answer is \( \boxed{0.015} \).