You measure the first qubit of the following state in the X basis and obtain |+>.
What is the state of the second qubit?
The given state can be rewritten in the X basis as:
Therefore, if |+> was measured for the first qubit, the second qubit will be in the |+> state too.
What does the following gate sequence simplify to (Ui means apply gate U to qubit i)?
It simplifies to: