4.He hasn't taken a bath  since last Monday
=> It is Monday when he last took a bath
=> The last time when he took a bath was Monday
=> He last  took a bath since  Monday

5. Her father hasn't taken her to the movies theater since she was at secondary shool.
=>It's when she was at secondary shool that her father hasn't taken her to the movies theater
=>The last time her father has taken her to the movies theater was when she was at secondary shool
=>Her father last took  her to the movies theater when she was at secondary shool