if it costs 25 cents to mail a letter weighing one ounce or less, and then 20 cents for each additional ounce or fraction of an ounce. Let L(x) be the cost of mailing a letter weighing x ounces. Graph y=L(x)

Let x be the weight of the letter.

L(x) = 0.25 + 0.20 (x-1).

X = 1, L(x) = y1 = 0.25
X = 2, L(x) = y2 = 0.45
X = 3, L(x) = y3 = 0.65
...

Create a graph. Plot these points (1, 0.25), (2, 0.45), (3, 0.65),.

If you know something about the equation for a line, you'll find this is very easy.