Okay, so F^-1 represents the reverse of a function. To get a reverse, simply switch the x and y variables and solve for x.
Ex: y = 2x to x = 2y to y = x/2, or y = 1/2x
We do the same thing for this problem.
y = 2x - 1
x = 2y - 1
2y = x + 1
y = (x + 1) / 2 = x/2 + 1/2 = 1/2x + 1/2
This is the correct graph because it is a graph of the reverse function
f^-1(x) = 1/2x + 1/2.
Hope this helps, let me know if I messed up!