When Sandra drives back home from work, she has to pass through two sets of traffic lights. The probability that she has to stop at the first is 0.35, while the probability that she has to stop at the second one is 0.40. Finally, the probability that she does not stop at a traffic light is 0.50. Calculate the probability that she has to stop

(i) at both sets of traffic lights;

(ii) at least at one set of traffic lights;

(iii) at exactly one set of traffic lights.