First-class mail retail flats weighing up to one ounce, plus $\"\"$ for each additional ounce up to $\"\"$ ounces.

The model that relates $\"\"$ , the first-class postage charged, for a flat weighing $\"\"$ ounces.

Write the piecewise function of the situation described in the problem.

$\"\"$

Graph of the function $\"\"$ .

$\"\"$ .

The function is,

$\"\"$

Graph of the function $\"\"$ .

$\"\"$ .