Choose any two points on the line and find the rate of change between them.

We will the points at (2, 10) and (4, 20).

(2, 10)2 iron weights, 10 lb total weight.

(4, 20)4 iron weights, 20 lb total weight.

Rate of change = .

The total weight changes from 10 lb to 20 lb and the iron weight changes from 2 to 4.

Rate of change =

Rate of change =

Rate of change = .               (Divide: )

So, the rate of change is , or a increase of 5 lb total weight per one iron weight.

The rate of change is .