1. The ratio of the area to the length of a rectangle is the rectangle (width). If the width is constant, the area of a rectangle is in direct proportion to its growth.

2. Dialing time per minute: 1, 2, 3, 4, 5, 6 ... Telephone charges: 0. 12, 0.24, 0.36, 0.48, 0.60, 0.72. ...

The expansion rule in the above table is (y=0. 12x, where y is the phone bill and x is the dialing time).