Answer:
4n -13
Step-by-step explanation:
notice that the difference between the adjacent terms is 4.
nth term is given by:
nth term = first term + (n-1) × difference -n is any number
= -9 + (n-1) × 4
= -9 + 4n -4
= 4n -13
x-15 = 8
add 15 to each side
x = 23