Answer:
an=a1+(n-1)*-6
Step-by-step explanation:
a1= 3
the recursive formula is an= a1+ (n-1)d
d= how you get from one to the other
to get from 3 to -18 you could either subtract 21 or multiply it by -6
to find which one you have to look at the next number which is 108
to get from -18 to 108 you would either add 126 or multiply it by -6
since multiplying by -6 is in both that is the answer
d= -6
an=a1+(n-1)*-6
