-3(x+(3))^2-4 is the answer
64838383848888477783839393
There are 6 other positions in the string, each with 26 choices. So if you fix BO as the first two letters, there are

possible strings that you can make.
If BO is at the end of the string, you still have

possible strings.
Together, then, you have

possible strings.
10 000
Anything greater than 5 rounds up
Hope this helps :)
C)
2n + 3
first term = 3
second term = 5 (2 + 3 = 5)
third term = 7 ( 4 + 3 = 7)
d)
term 15 that has value greater than 30
cause
2(14) + 3 = 28 + 3 = 31 greater than 30