Final answer:
The postage for first-class letters weighing 3.5 oz or less can be expressed as a piecewise defined function based on weight.
Step-by-step explanation:
The postage for first-class letters weighing 3.5 oz or less can be expressed as a piecewise defined function based on weight. Let's denote the weight of the letter as x.
For 0 < x ≤ 1, the postage is $0.49.
For 1 < x ≤ 3.5, the postage is $0.49 + $0.21(x-1).
So, the piecewise defined function for the postage is:
P(x) =
$0.49 if 0 < x ≤ 1
$0.49 + $0.21(x-1) if 1 < x ≤ 3.5