What are two things that need to be true in order to combine terms together

The equation represents the function f, and the graph represents the function g. f(x)=3(5/2)^x determine the relationship between the growth factors of f and g. a. the growth factor of g is twice the growth factor of f. b. the growth factor of f is twice the growth factor of g. c. the growth factor of f is 2.5 times the growth factor of g. d. the growth factor of f is the same as the growth factor of g.