a) From the given data we get that the doctors that have treated more than 900 male patients are:
Kidd, Li, Boyd, Cruz, and Falce.
b) From the given data we get that the doctors that have treated more than 1400 female patients are:
Kidd, and Li.
Answer:
(a) {Kidd, Li, Boyd, Cruz, Falce}.
(b) {Kidd, Li}.