**Solution:**

Let’ say

Event that surgeries are rated as very complex

Event that surgeries are rated as complex

Event that surgeries are rated as routine

Event that surgeries are rated as simple

Event that surgeries are rated as very simple

Given that

(a) (routine or complex)

By General Addition Rule]

[given

(b) (routine or simple)

By the General Addition Rule]

[as given

(a) routine or complex

(b) routine or simple

(a) routine or complex

(b) routine or simple