It's a line so its equation is in the form : y = mx + b where m is the slope/gradient and b the y-intercept.
Since the slope m here is -1/4, we can write :
y = (-1/4)x + b
And since that line passes through the point x=-2, y=6, we can find the y-intercept by solving this equation of unknown b :
b + (-1/4)*(-2) = 6
b = 6 - (-1/4)*(-2)
b = 6 - (2/4)
b = 6 - 1/2
b = (12-1)/2 = 11/2
Finally, the equation is y = (-1/4)x + 11/2
