Which rule can be used to describe the growth of the y-values of the function y=12^x over each interval from x=-1 to x=3?

"Which rule ..." suggests you have some rules to choose from to describe the growth. Since you refer to "each interval from x=-1 to x=3", we assume your rule is concerned with more than one interval. With no further clues as to what you may be looking for, we can compute the factor by which the function grows from x=-1 to x=3.The growth factor over that interval is the ratio of final value to initial value: .. (12^3)/(12^-1) = 12^(3 -(-1)) = 12^4 = 20,736