[Alan Anderson]

The line on the carpet is not made of the expensive retroreflective material. It is 2-inch-wide gray gaffer's tape.

The easiest way to follow a line is to have two sensors not quite as far apart as the tape is wide. When neither sees the tape, turn right. When the right one sees the tape, go straight. When the left one sees the tape, turn left. If you want to detect the end-of-line mark, use a third sensor to the left of the others. When all three see the tape, stop. This will follow the left edge of the line. It should be obvious how to change it to follow the right edge if you want to.