Interpretation of these physician orders

Hi....i know this is just a bonehead nursing student question...but yesterady our instructor tested us on paper on how to interpret these physicians orders:

1) Salbutamol 1 nebule via USN now X 3 doses then every 30 minutes

My interpretation: It means that I should give a salbutamol inhalation as a STAT dose then I should give 3 more doses continously without intervals (e.g. 15 minutes, 30 minutes) then I should give the medication every 30 minutes after my 3rd dose...

Is this correct?...or did I miss something

Also, when giving the inhalation following the 30 minute interval when should I start counting my 30 minutes:

A. After the inhalation was complete ( e.g 9:30 inhalation was given; 9:45 inhalation was finished then I should give the med at 10:15?)

or

B. Should I start counting from the time that I have given the dose (started 9:30, finished 9:45 give the next dose at 10:00?)

Which one should I follow?....

2. Situation: Shift Cefuroxime 750 mg IV push to Ceftriaxone 1 gram IV push q8hrs ANST

Cefuroxime last given: 8:00 Am

My interpretation: Disconinue the Cefuroxime...Do the skin test for Ceftriaxone then wait until 4:00 P.M. to give

the initial dose dose...

Am I correct?...

Man, eventhough I have answered my instructors questions but I have that lingering doubt that there is something wrong on my answers...

Could someone help me please?...

Thank you...