The answer is -1/4
Firstly you make a triangle on the line by plotting the points on where the line meets a point or coordinate.
Looking at the triangle, you will see that it goes up by 1 (the rise part) and it goes along by 4 (the run part)
rise/run = 1/4
The line is negative because if it went in the opposite direction, it would be positive, making the gradient or slope -1/4.
Sorry if that didn’t make sense