Answer:
t(n+1) = t(n) +9
Explanation:
Let the Term position be represented by n.
and term value is represented by t.
so term value at any position can be represented by t(n).
Here look closely
t(1)=3, t(2)=12, t(3)=21, t(4)=30
By examining, we notice that the next term is 9 more than the previous one.
e.g
t(2)= t(1)+9
3+9
t(2)=12
t(3) = t(2)+9
t(3) = 21
we can represent them in mathematical form as:
t(n+1) = t(n) +9