Two part question

What is the maximum amount that can be ported to Husband #2 if the DSUEA of deceased Husband #1 was $2.0 million and his wife remarries in 2013 to Husband #2 with her full exemption amount of $5.43 million available when wife dies in September 2015 and leaves everything to Husband #2, except for $1 million to her children?

(A) $7.43 million

(B) $6.43 million

(C) $5.43 million

Same facts as about question, but what if Husband #2 has made significant lifetime gifts of $3 million to his children from a prior marriage, how much applicable credit will he have if he died in December 2015?

(A) $7.43 million

(B) $8.43 million

(C) $2.43 million

Can you provide a detailed explanation for your answer? Please only answer if you have a strong background in estate planning.