The formula for slope is y = mx + b
y is the y value, m is the slope, x is the x value, and b is the y intercept.
The equation given for line e is 

Therefore the slope of line e is -9/2
Line f is parallel and parallel lines have the same slope.
So the slope is line f is -9/2.
The picture isn't that clear and I can't really tell if it's-9/2 or 9/2. 
But whatever it is, the slope of line f is the same as the slope of line e because they are parallel. 
Good luck!