Answer:
Yes, they vary directly
Step-by-step explanation:
y=kx; k is the constant (12 in this case) and as x increases y increases, so they vary directly
 
        
             
        
        
        
The vertices of the triangle are the points where any pair of lines intersect.
We start by setting up the system

Using one of the two equations we can derive the correspondent y value:

So, one vertex is (1, 1)
We choose the other two pairs of lines to find the other vertices:


So, the three vertices are (1, 1), (2, 0), (-1, -3).