12. The acute angle or right angle formed by the intersection of two lines is called the "angle" between the two lines. Now there are several lines on a plane, they intersect each other in pairs, and the "angle" can only be $30^{\circ}, 60^{\circ}$, or $90^{\circ}$. Question: What is the maximum number of lines?
12. There are at most 6 lines.
12. [Solution] There are at most 6 lines, as shown in the figure: