What is the negative of -1/3 and why? ?

Thus, the negative of negative 1/3 is 1/3.

You would graph the two equations and the point of intersection is your answer. The slope for y=2x-1 is 2 and the y-intercept is found when x=0, so the y-intercept is  y=2(0)-1   y=-1. The slope for y=4x-5 is 4.  The y-intercept is y=4(0)-5   y=-5
If you don't want to graph to solve the system of equations, ou can set them euqal to each other and solve for the variables:
2x-1=4x-5  >   2x=4x-4  >   -2x=-4  >   x=2
y=2(2)-1  >   y=4-1  >   y=3
y=4(2)-5  >   y=8-5  >   y=3
So x=2 and y=3, so the solution is  {2,3}