The domestic postage rate for first-class letters weighing 3.5 oz or less is 39 cents for the first ounce (or less), plus 16 cents for each additional ounce (or part of an ounce).
Express the postage P in dollars as a function of the weight x of a letter, with 0 < x ≤ 3.5, and sketch the graph of this function.
P(x) = $
if 0 < x ≤ 1 $
if 1 < x ≤ 2 $
if 2 < x ≤ 3 $
if 3 < x ≤ 3.5