Am I a resident alien or a dual status alien?

My situation is

F1: 2016 August---2019 February 17 

H1b: 2019 February 18- 2019 Dec 31

My understanding is that I met the Substantial Presence Test of 183 days as a resident alien.  But in January and February because I'm an exempt individual, I was a non-resident alien. Therefore, I have to file as a dual status. Is this correct? 

If this is correct, here comes to another question. I worked for the same company for the whole 2019 and received one W2.  How can I determine what amount is for non-resident and what for resident? Do I just probate by month?