The equation is y = 2x -1 and as you know it should be y = mx - c

so c here is -1 this excludes the upper two choices

now the lower ones are both passing through -1 so now we look at any point

for example if I look at the lower left at x = 5 according to our equation y = 2(5)-1=9 but their graph has only 1.5 ...nope bad choice

The bottom right is our graph

And how to find the gradient