The cost $C$ of sending a parcel post package weighing $P$ pounds, where $P$ is an integer, is $10$ cents for the first pound and $3$ cents for each additional pound. What is the formula for the cost $C$ in terms of $P$? The original answer is in the form $C = a + b(P - 1)$, please give the value of $a + b$.

Let's think step by step and output the final answer within \boxed{}.
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