Mark M. answered 04/15/21
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
Recall that f'(x) = limh→0 [(f(x+h - f(x)) / h]
Let f(x) = ex. So, f(x+h) = ex+h.
Then, limh→0 [5(ex - ex+h) / (3h) ] = -(5/3)limh→0 [(ex+h - ex) / h ] = -(5/3)(ex)' = -(5/3)ex