1-. The courts use the lemon test that is a three part test that determines if a law violates the establishment clause . The three  parts are  1. The law must have a purpose , 2. The primary effect of the law must be neither to advance nor to inhibit religion and finally . 3. The law must not result in a entanglement of government and religion 

2-. In the 1989 case of Texas vs  Johnson the court ruled that the burning of a flag is a form of symbolic speech and it is protected by the first amendment so the burning of the US flag is protected by the first amendment

3-. I’m taking the fifth means that I will stay silent and refuse to answer any questions until I am with my lawyer.