When we have dependent and independent variables we will have a linear relationship. 
Let x be the independent variable and y be the dependent variable. 
To write the relationship we will have :
y = kx + c
Where k and c are constants.
In the case of a line the constant k is the gradient. 
A multiplicative change is a log form and it is given by :
Y = Ck^x
The relationship is not linear but exponential. 
The correct answer is thus :
Additive rate of change.