How to make a offset lines for the lines showing an area 40% smaller than the site area

[shimizu3L5L3]

Please help me!!
i want to make a line with an area reduced by 60% but i can’t find a way(on working now) because I’m beginner…
That’s why please teach me how to make it.

[BimAmbit]

Something along this line:

[shimizu3L5L3]

Thank you again @BimAmbit !!!
I’ll try this!