(a) The function \( P(d) \) is:
\[
\boxed{P(d) = 0.433d + 14.7}
\]
(b) The correct function notation for the pressure at the depth of the Titanic is:
\[
\boxed{\text{C. } P(12{,}500)}
\]
(c) The pressure at a depth of \( 2095 \, \text{ft} \) is:
\[
\boxed{920.84 \, \text{lbs/in}^2}
\]