I doubt there is any "formula" established for this but here is what I would do:

Suppose the total time available to take calls is T seconds. Since team 1 take 195 seconds per call, team 1 can answer T/195 calls. Since team 2 takes 205 seconds per call, team 2 can answer T/205 calls. Since team 3 takes 215 seconds per call, team 3 can answer T/215 calls.

That would be a total of T/195+ T/205+ T/215 calls. If you like those fractions can be added as ((205)(215)T+ (195)(215)T+ (195)(205)T)/(195+ 205+ 215)= [((205)(215)+ (195)(215)+ (195)(205))/(195+ 205+ 215)]T calls. Set that equal to 100 and solve for T. Once you have that T/195, T/205, and T/215 give the number of calls each team handled.