e is an int probably. There are multiple overloads of pow (one takes a double, another takes a float, and another takes a long double). e can be cast into any one of these so the compiler does not know which one to choose. Try making it so e is one of double, float, or long double.
Then maybe the conflict is coming from exponent? If that's also a double (which I assumed it was) then there wouldn't be a problem. Can you post the rest of the code (including the initializations of rate, e, and exponent?
Casting should make the compiler error go away, regardless: