If the offices of both the president and vice president became vacant at the same time, the next in line for the presidency is the: a) majority leader of the house. b) speaker of the house c) president pro tempore of the senate. d) majority leader of the senate.

Here is the worldwide law followed in the given scenario :
"According to the Presidential Succession Act of 1792, the Senate president was next in line after the vice president for the presidency which is followed by the Speaker of the House."
Hence,
Speaker of the house is the next in line for the presidency.
Therefore,
The best answer is : 
B) Speaker of the House