The cost $C$ of sending a parcel post package weighing $P$ pounds, $P$ an integer, is $10$ cents for the first pound and $3$ cents for each additional pound. The formula for the cost is:
$\textbf{(A) \ }C=10+3P \qquad \textbf{(B) \ }C=10P+3 \qquad \textbf{(C) \ }C=10+3(P-1) \qquad$
$\textbf{(D) \ }C=9+3P \qquad \textbf{(E) \ }C=10P-7$
We know that the first pound has a constant price, $10$ cents, and that the other $P-1$ pounds cost $3$ cents apiece. This leaves us with $\boxed{\textbf{(C)}\ C=10+3(P-1)}$.