How do you make parallel lines for parking lots

One of my questions in my geometry homework is this, "your company, StripeMasters, is hired to paint the parallel parking spots at a shopping center. Write a Mel-Con describing your process to guarantee that the lines in each row are actually parallel."

Draw a chalk line perpendicular to the direction of the intended parallel lines and make its length '3 units' e.g. 6 feet i.e 3 x 2 feet.
Now cut two pieces of string: one 'four units' and one 'five units' e.g. 8 and 10 feet (4 x 2', 5 x 2').
Use these to mark out a 3 by 4 by 5 triangle. One of the angles will be exactly perpendicular to your first '3 unit' line.
Repeat this but swap over the 4 and 5 unit strings so that the perpendicular is made at the other end of the original '3 unit' line.
Now you will have two parallel '4 unit' lines marked on the ground that are each exactly perpendicular to the original '3 unit' line.

Two simple tools are required - after you have a scaled drawing of how the lines are to be painted - a long ruler and a chalk line.

Start out by measuring where the first line is to be made, measure and mark both ends. Then snap the chalk line between those points. Then measure the width of the parking space over, mark the ends and snap the chalk line again. Repeat until the lot has been marked. Now load your paint machine and follow the chalk lines.