H1b transfer while H1b extension filed

[sunnyroyer]

I am working full time, with company A. My visa is Valid with Company A till March2018.

While my H1b extension is pending approval, if I decide to move to company B, who file my h1b transfer, then,

(a)    If the h1b transfer from company A to company B happens successfully, say in December, would h1B with new company B be valid beyond March2018, and if yes, what happens to h1b extension With company A being done?

(b)    If the h1b transfer from company A  to company B happens successfully, say in December, if the  h1B with new company B is  valid only through  March 2018, then can the h1b extension with A  be allowed to finish? 

Thanks.

All responses appreciated.

Sunny