You will need to be able to solve a system of two equations
in two variables to do this problem.  If you don't know how
to do that post again asking how.

I will color-code the equations and their graphs:






We want to find the three vertices, the vertices A,B, and C
of triangle ABC  (points where two line intersect):

To find the vertex where the red and green lines intersect, 
solve this system:



Solve them by substitution and get (1,4)


To find the vertex where the red and blue lines intersect, 
solve this system:



Solve them by substitution and get (2,0)

To find the vertex where the red and green lines intersect 
by solving this system:



Solve them by substitution and get (,)




Edwin