What does non-linear mean

Scenario: susan wants to make 2 square flags to sell at a crafts fair. the fabric she wants to buy is 3 meters wide. she doesn't want any fabric left over. what's the least amount of fabric she should buy? question: which equation will susan solve her problem? note: let x represent the length of 1 side of the flag. options: 1) 3x^2 -2x =0 2) 2x^2 =3x 3) 2 * 2 = 2 * 2 4) 6 +2x = 2(4x)