B:  0.492
Explanation:
No, this is not correct.
It is good that you realised the angle given in the question is not with the positive x-axis. You correctly found the angle that the line makes with the positive x-axis; however, you forgot to change the mode on your calculator to degree mode as the angle given is in degrees, not radians.
C: 0.511
Explanation:
No, this is not correct.
The angle in the graph is made by the line and the negative x-axis, not positive x-axis
From Gradient formula #3: