What value of c makes x^2+6x+c a perfect square trinomial

Adriver from the university of florida women’s swimming and diving team is competing in the in ncaa zone b championships

What is the value of x in the this question ?

Pepe and leo deposits money into their savings account at the end of the month the table shows the account balances. if there pattern of savings continue and neither earns interest nor withdraw any of the money , how will the balance compare after a very long time ?