Who informs congress if the president cannot carry out the duties of the office?

the vice president
the president's cabinet
the president
the president's spouse

If the president cannot or will not inform the congress by him/herself, the Vice President informs the congress along with majority of cabinet members in written form.

Explanation:

In case the president cannot carry out the 'duties' the Vice President assumes the presidency and carry out the 'duties'. Only the Vice President can inform the congress about the Presidents inability to perform his/her duties, majority of cabinet officers must also agree on that. In case the 'Vice President' cannot assume the presidency, speaker of house is next in line.