Gradient is the difference between the y-axis and the x-axis 
Gradient = y2-y1/x2-x1 
Choose any two point making a triangle 
Line B (0,8) (4,0) 
This makes a triangle please go look at the graph once again! The the triangle should not have half squares but full! 
Line A (5,14)(2,2)
Now plug in the variable 
The difference between the Y and X
Line B 0-8/4-0  
Line B gradient =-2 
Line A 2-14/2-5
Line A gradient = +4 
Finalized answer 
Line B gradient = -2 
Line A gradient = +4