Given data:
The first value of x is a=-16.
The first value of y is b=20.
The second value of x is c=-12.
The second value of y is d=15.
The expression for the rate change is,
x=(d-b)/(c-a)
Substitute the given values in thhe above expression.
x=(15-20)/(-12+16)
=-5/4
Thus, he constant rate of change is -5/4.